# List of Greek and Latin roots in English/O

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## O

| Root | Meaning in English | Origin language | Etymology (root origin) | English examples |
| ob-, o-, oc-, of-, og-, op-, os- | against | Latin | ob | obduracy, obdurate, obduration, obfuscate, oblique, obliquity, obstinate, obstreperous, occur, offend, omit, oppose, ostensible, ostentatious |
| obel- | spit, nail | Greek | ὀβελός (obelós), ὀβελίσκος (obelískos) | metobelus, obelisk, obelism, obelus |
| obol- | nail | Greek | ὀβολός, ὀβολοῦ (obolós, oboloû) | obol, obolus |
| ocean- | river, stream | Greek | ὠκεανός (ōkeanós) | Oceania, oceanic |
| ochl- | crowd, mob | Greek | ὄχλος, ὄχλου (ókhlos, ókhlou) | enochlophobia, ochlocracy, ochlophobia |
| oct- | eight | Greek | ὀκτώ (oktṓ), ὀκτάς (oktás), ὀκτάκις (oktákis) "eight times" | hemi-octahedron, octad, octadic, octagon, octahedron, octameter, octode |
| oct- | eight | Latin | octō | octangular, octennial, octovir |
| octav- | eighth | Latin | octāvus | octaval |
| octogen- | eighty each | Latin | octogeni | octogenarian, octogenary |
| octogesim- | eightieth | Latin | octogesimus | octogesimal |
| octon- | eight each | Latin | octoni | octonary |
| ocul- | eye | Latin | oculus, oculare | ocular, oculus, ullage |
| od- | path, way | Greek | ὁδός (hodós) | anode, diode, odometer, parodos, pentode, tetrode, triode |
| odi- | hate | Latin | odium | odious |
| odont- | tooth | Greek | ὀδούς, ὀδόντος (odoús, odóntos) | anodontia, conodont, cynodont, dicynodont, dysodontiasis, macrodontia, mastodon, odontoid, odontology, odontophore, orthodontics, orthodontist, pedodontics, periodontal, smilodon, Thrinaxodon, Zanclodon |
| odor- | fragrant | Latin | odor | malodorous, odoriferous, odorous |
| odyn- | pain | Greek | ὀδύνη (odúnē) | allodynia, anodyne, glossodynia, mastodynia, pleurodynia |
| oec- | house | Greek | ϝοῖκος (woîkos), οἶκος (oîkos) | andromonecy, archdiocese, autoecious, autoecism, dioecious, dioecy, ecesis, ecologist, ecology, economics, economist, economize, economy, ecoregion, ecosystem, ecumenic, ecumenism, gynomonoecy, heteroecious, heteroecism, heteroecy, homoecious, monoecious, monoecy, oecology, oeconomus, oecumenic, oikology, oikophobia, palaeoecology, paleoecology, parish, paroecious, perioeci, trioecious |
| oed-, ed- | swell, swollen | Greek | οἶδος (oîdos), οἰδεῖν (oideîn), οἴδημα, οἴδηματος (oídēma, oídēmatos) | angioedema, edema, edematous, oedema, oedematous |
| oen- | wine | Greek | ϝοῖνος (woînos), οἶνος (oînos) | enology, oenochoe, oenologist, oenology, oenophile, oenophilia, oinochoe |
| oesophag- | gullet | Greek | οἰσοφάγος (oisophágos) | oesophagectomy, oesophagitis, oesophagus |
| oestr- | gadfly, sting | Greek | οἶστρος (oîstros), οἰστράω, οἴστρησις, οἴστρημα | anestrous, anestrus, anoestrus, estrogen, estrogenic, estrus, oestrone, oestrus |
| ogdo- | eighth | Greek | ὄγδοος (ógdoos), ὀγδοάς, ὀγδοάδος (ogdoás, ogdoádos) | ogdoad |
| -oid | like | Greek | -οειδής (-oeidēs) | asteroid, mucoid, organoid |
| ole- | oil | Latin | oleum | oleosity |
| olecran- | skull of elbow | Latin from Greek | ὠλέκρανον (ōlékranon) | olecranon |
| olig- | few | Greek | ὀλίγος (olígos) | oligarchy, Oligocene, oligopoly, oligosaccharide, oligotrophic |
| oliv- | olive | Latin | oliva | olivaceous, olivary, olivette |
| om- | raw | Greek | ὠμός (ōmós), ὠμότης (ōmótēs) "rawness" | omophagia, Omophagus |
| om- | shoulder | Greek | ὦμος (ômos), ὠμία (ōmía) | acromion, omohyoid, omophorion |
| -oma | morbid growth, tumor | Greek | -ωμα | melanoma |
| omas- | paunch | Latin | omasum | abomasum, omasum |
| ombr- | rain | Greek | ὄμβρος (ómbros) | ombrogenous, ombrology, ombrometer, Ombrophila, ombrophilous, ombrophobe, ombrotrophic |
| oment- | fat skin | Latin | omentum | omental |
| omin- | creepy | Latin | omen, ominis | abominable, ominous |
| ommat- | eye | Greek | ὁράω, ὦμμαι, ὄμμα, ὄμματος (ómma, ómmatos) | ommatidium, ommatophore |
| omni- | all | Latin | omnis | omnipotence, omnipresent, omniscient, omnivore |
| omphal- | navel | Greek | ὀμφαλός (omphalós) | omphalectomy, omphalic, omphalopagus, omphalophobia, paromphalocele |
| on- | ass | Greek | ὄνος (ónos), ὀνίσκος (onískos) | Oniscidea, Oniscomorpha |
| onc- | barb, hook | Greek | ὄγκος, ὄγκινος (ónkinos) | Oncinocalyx, Oncorhynchus |
| onc- (ΕΓΚ) | bulk | Greek | ἐνεγκεῖν, ὄγκος (ónkos), ὀγκόω, ὀγκωτός, ὄγκωσις, ὄγκωμα | oncocyte, oncocytoma, oncogenesis, oncologist, oncology |
| oneir- | dream | Greek | ὄνειρος (óneiros), ὀνειρώσσω, ὀνείρωξις (oneírōxis) | oneiric, oneirism, oneirocritic, Oneirocritica, Oneirodidae, oneirogen, oneirogenic, Oneiroi, oneiroid, oneirology, oneiromancy, oneironaut, oneironautics, oneirophobia, oneirophrenia, oneiroscopy |
| oner- | burden, load | Latin | onus, oneris | exonerate, exoneration, onerous, onus |
| oni- | price | Greek | ὦνος (ônos), ὤνιος (ṓnios) | oniochalasia, oniomania, oniomaniac |
| onomat- | name | Greek | ὄνομα, ὀνόματος (ónoma, onómatos), ὀνομάζω, ὀνομαστικός (onomastikós) | antonomasia, onomasiology, onomastic, onomasticon, onomastics, onomasty, onomatology, onomatophore, onomatopoeia |
| ont- | being, existence | Greek | ὄντος, ὀντότης (óntos, ontótēs), οὐσία (ousía) | dysontogenesis, homoiousia, homoousia, monoousious, ontogenesis, ontogenetic, ontogeny, ontology, ousia, parousia |
| onych- | claw | Greek | ὄνυξ, ὄνυχος (ónux, ónukhos), ὀνύχιον (onúkhion), ὀνύχινος, ὀνυχίζω | hapalonychia, Mesonychia, onychectomy, onycholysis, onychomancy, onychomycosis, onychophagia, onychophagy, onychorrhexis, onyx, paronychia, sardonyx |
| onym- | name | Greek | ὄνυμα (ónuma) | acronym, allonym, anonymous, antonym, autonym, caconym, cryptonym, eponym, eponymous, eponymy, euonym, homonym, hyperonym, hyponym, hyponymy, meronym, meronymy, metonym, metonymy, metronymic, paronym, paronymous, pseudonym, pseudonymous, synonym, synonymous, synonymy, tautonym, tautonymous, tautonymy, troponym, troponymy, xenonym, xenonymy |
| oo- | egg | Greek | ᾠόν (ōión) | bottarga, dioon, epoophoron, oidioid, oidium, ooblast, oocyst, oocyte, oocytogenesis, oogamete, oogamous, oogamy, oogenesis, oogonium, ooid, oolite, oolith, oology, oomancy, oophagy, oophorectomy, oophoron, ootheca, ootid, ootidogenesis, paroophoron |
| op- | hole | Greek | ὀπή (opḗ), ὀπαῖον (opaîon) | metope, opaion |
| opac- | shady | Latin | opacus | opacity, opacus, opaque |
| oper- | work | Latin | opus, operis | cooperate, inoperable, opera, operate, opus |
| oper- | cover | Latin | operire, operculum | interoperculum, kerchief, opercular, operculiform, operculum |
| ophi- | snake | Greek | ὄφις, ὄφεως (óphis, ópheōs) | Brachyurophis, ophicephalous, Ophicephalus, Ophiceras, Ophiclinus, ophidiophobia, ophiolite, ophiologist, ophiology, ophiophagous, Ophiophagus, ophiophagy, ophiophobia, Ophisaurus, Ophisops, ophitic |
| ophthalm- | eye | Greek | ὀφθαλμός (ophthalmós) | exophthalmic, exophthalmos, microphthalmia, ophthalmia, ophthalmic, ophthalmologic, ophthalmologist, ophthalmology, ophthalmoparesis, ophthalmoplegia, parophthalmia, xerophthalmia |
| opisth- | behind | Greek | ὄπισθεν (ópisthen), ὀπίσθιος | anopisthograph, opisthion, opisthobranch, opisthodomos, opisthoglyphous, opisthognathous, opisthograph, opisthokont, opisthosoma, opsimath, opsimathy |
| ops-, opt- (ΟΠ) | eye | Greek | ὄψεσθαι (ópsesthai), ὀπτός (optós), ὀπτικός (optikós), ὄψις (ópsis) | amblyopia, anopia, autopsy, biopsy, catadioptrics, catoptrics, catoptromancy, catoptrophobia, cyclops, diopter, dioptre, dioptrics, diplopia, eisoptrophobia, emmetropia, hemianopsia, myopia, opsoclonus, optic, optokinetic, panopticon, pleoptics, synopsis, synoptic, tritanopia |
| opsi- | late | Greek | ὀψέ (opsé), ὄψιος | opsimath |
| opson- | cook, prepare for eating | Greek | ὀψωνεῖν (opsōneîn), (opsōnia) | opsonin, opsonoid |
| opt- | choose | Latin | optare | adopt, adoptee, adoption, adoptive, co-option, coopt, cooptation, nonoptional, opt, optation, optative, option, optional, optionality |
| optim- | best | Latin | optimus | optimal, optimum |
| or-, oro- | mountain | Greek | ὄρος, ὄρεος (óros, óreos), ὀρειάς | Oread, orogenesis, orogenic, orogeny, orographic, orography, oronym |
| or- | mouth | Latin | os (genitive oris) "mouth" | adosculation, inosculate, inosculation, interosculate, intraoral, oral, orifice, osculant, osculum, peroral |
| ora- | pray, plead | Latin | orare "to pray, plead" | adore, adoration, exorable, inexorable, oracle, orate, oration, orator, oratorio, oratory, orison, perorate, peroration, perorator |
| orb- | circle | Latin | orbis | orbit |
| orch- | testicle | Greek | ὄρχις (órkhis), ὀρχίδιον (orkhídion) | anorchia, cryptorchidism, monorchism, orchid, orchiectomy, orchiopexy, Orchis, polyorchidism |
| orches- | dance | Greek | ὀρχεῖσθαι (orkheîsthai) | orchestra |
| ordin- | order | Latin | ōrdō, ordinis | coordinal, coordinate, coordination, coordinator, disorder, extraordinaire, extraordinary, grandorder, incoordinate, incoordination, infraorder, inordinate, inordination, insubordinate, insubordination, magnorder, mirorder, ordain, ordainment, order, ordinal, ordinance, ordinand, ordinariate, ordinary, ordinate, ordination, ordinative, ordnance, ornery, parvorder, preordain, preorder, preordination, quasiorder, reordain, reorder, reordination, suborder, subordinary, subordinate, subordination, superordain, superorder, superordinate, superordination |
| oreg- | reach | Greek | ὀρέγειν (orégein), ὀρεκτός (orektós), ὀρεκτικός (orektikós), ὄρεξις (órexis), ὄρεγμα (óregma) | anorectic, anorexia, dysorexia, orectic, orexin, parorexia |
| org- | work | Greek | ὄργια (órgia) | orgasm |
| organ- | organ, instrument, tool | Greek | ὄργανον (órganon) | organic, organism, organogenesis |
| ori-, ort- | rise | Latin | oriri, ortus | aboriginal, abort, abortifacient, abortion, abortive, disorient, disorientation, orient, oriental, Orientalia, orientate, orientation, orientational, orientative, origin, original, originality, originate, origination, originator, reorient, reorientation |
| orn- | decorate | Latin | ōrnāre | adorn, adornment, ornament, ornamental, ornamentation, ornate, ornative, ornature, suborn, subornation |
| ornith- | bird | Greek | ὄρνις, ὄρνιθος (órnis, órnithos) | Avernus, ornithology, ornithomancy, ornithorhynchus, ornithosis |
| orphan- | | Greek | ὀρφανός (orphanós), ὀρφανότης | orphan |
| orth- | straight | Greek | ὀρθός (orthós), ὀρθότης | orthocenter, orthocentric, orthodontia, orthodontic, orthodontist, orthodox, orthodoxy, orthographic, ortholog, orthologous, orthonym, orthopedic, orthoscope, orthosis, orthostat, orthostyle, orthotic |
| oryz- | rice | Greek | ὄρυζα (óruza), ὀρύζιον | Oryza, Oryzomys, rice, risotto |
| oscill- | swing | Latin | oscillum | oscillate, oscillation, oscillator, oscillatory |
| osm- | odor | Greek | ὀσμή (osmḗ), ὄσμησις | anosmia, anosmic, cacosmia, coprosmia, dysosmia, dysosmic, euosmia, hyperosmia, hyperosmic, hyposmia, hyposmic, osmium, osmolagnia, osmophobia, osphresiolagnia, parosmia, phantosmia, troposmia |
| osm- | push, thrust | Greek | ὠσμός (ōsmós) | osmometry, osmosis, osmostat, osmotic |
| oss- | bone | Latin | os, ossis | exossation, interosseous, ossature, osselet, osseocartilaginous, osseointegration, osseous, ossicle, ossicular, ossiferous, ossification, ossifrage, ossify, ossuary |
| oste- | bone | Greek | ὀστέον, ὀστέου (ostéon, ostéou), ὀστοῦν, ὀστοῦ (ostoûn, ostoû) | dysostosis, endosteum, exostosis, hyperostosis, monostotic, Osteichthyes, osteoarthritis, osteoblast, osteochondritis, osteochondrosis, osteoclast, osteogenic, osteogenesis, osteoid, osteology, osteolysis, osteoma, osteomalacia, osteonecrosis, osteopathy, osteopenia, osteoporosis, osteosarcoma, osteosis, osteothrombosis, osteotome, osteotomy, periosteum, synostosis |
| osti- | entrance | Latin | ostium | ostiary, ostiolar, ostiole, ostium |
| ostrac- | shell | Greek | ὄστρειον (óstreion), ὀστρακίζω (ostrakízō), ὄστρακον (óstrakon) | Entomostraca, Leptostraca, Malacostraca, ostracism, ostracize, ostracod, ostracoderm, ostracon, periostracum |
| ostre- | oyster | Greek | ὄστρεον | ostreophagist, oyster |
| ot- | ear | Greek | οὖς, ὠτός (oûs, ōtós) | anotia, Aotus, microtia, Myosotis, otalgia, otic, otitis, otocephaly, otocleisis, otoconium, otocyst, otodynia, otolith, otology, otopathy, otophyma, otoplasty, otorhinology, otorrhea, otosclerosis, otoscope, otoscopy, ototomy, parotic, parotid, periotic, synotia |
| ov- | egg | Latin | ovum | obovate, oval, ovarian, ovariole, ovary, ovate, ovicapsule, ovicidal, ovicide, oviduct, oviferous, oviform, oviposition, ovipositor, ovolo, ovular, ovulation, ovulatory, ovule, ovum, pluriovulate |
| ovi- | sheep | Latin | ovis | ovile, ovine |
| oxy- | sharp, pointed | Greek | ὀξύς (oxús) | anoxia, anoxic, dioxide, hypoxia, monoxide, oxide, oxyanion, oxygen, oxyhalide, oxymoron, oxyntic, oxytone, paroxysm, pentoxide, polyoxide, tetraoxygen, tetroxide, trioxide |
| oz- | smell | Greek | ὄζειν (ózein), ὄζων (ózōn), ὄζη | ozocerite, ozone, ozopore |