octave
An interval of twelve semitones spanning eight degrees of the diatonic scale, representing a doubling or halving in pitch frequency.
The pitch an octave higher than a given pitch.
A coupler on an organ which allows the organist to sound the note an octave above the note of the key pressed (cf sub-octave)
A poetic stanza consisting of eight lines; usually used as one part of a sonnet.
The eighth defensive position, with the sword hand held at waist height, and the tip of the sword out straight at knee level.
The day that is one week after a feast day in the Latin rite of the Catholic Church.
An eight-day period beginning on a feast day in the Latin rite of the Catholic Church.
A small cask of wine, one eighth of a pipe.
An octonion.
Any of a number of coherent-noise functions of differing frequency that are added together to form Perlin noise.
The subjective vibration of a planet.

octocentenary
An eight-hundredth anniversary.

octoedrical
octahedral

octofarious
In eight ranks or rows.

octogenaries
plural of octogenary

octogenary
Of or related to the number 80, particularly
Of or related to the number 80, particularly

octogonal
Obsolete form of octagonal.

oculomotory
Archaic form of oculomotor.

odible
Fit to excite hatred; hateful, odious.

odontographic
Of or pertaining to odontography.

odontophorous
odontophoral.

odorate
odorous

odorates
plural of odorate

odouriferous
Obsolete form of odoriferous.

oecumenic
Archaic form of ecumenic.

oesophagean
Alternative form of esophagean.

offenceful
offensive

offencive
Obsolete form of offensive.

offenseful
offensive; displeasing.

officinal
Medicinal.
Used in a shop, or belonging to it.
Kept in stock by apothecaries; said of such drugs and medicines as may be obtained without special preparation or compounding; not magistral.

officious
Obliging, attentive, eager to please.
Offensively intrusive or interfering in offering advice and services.

offscum
Refuse; scum.

offscums
plural of offscum

often
Frequently; many times on different occasions.

oftentime
(elsewhere, archaic) Synonym of oftentimes.

og
Initialism of own goal.

ogs
plural of og

old
Of an object, concept, relationship, etc., having existed for a relatively long period of time.
Of an object, concept, relationship, etc., having existed for a relatively long period of time.
Of an object, concept, relationship, etc., having existed for a relatively long period of time.
Of an object, concept, relationship, etc., having existed for a relatively long period of time.
Having been used and thus no longer new or unused.
Having existed or lived for the specified time.
Of an earlier time.
Of an earlier time.
Of an earlier time.
Of an earlier time.
Of an earlier time.
Tiresome after prolonged repetition.
Said of subdued colors, particularly reds, pinks and oranges, as if they had faded over time.
A grammatical intensifier, often used in describing something positive, and combined with another adjective.
Indicating affection and familiarity.
Designed for a mature audience; unsuitable for children below a certain age.
Excessive, abundant.

oldass
Used in the same context as old, but more intense.

olde
Archaic spelling of old.

older
comparative form of old: more old, elder, senior

oldermost
Oldest.

oldest
superlative form of old: most old

oldests
plural of oldest

oldfangled
old-fashioned

oldfashioned
Rare form of old-fashioned.

oldish
somewhat old

olds
One's parents.
Anyone portrayed in the context as not young; for example, anyone older than the speaker's audience of coevals; often, middle-aged adults or older adults.

oldschool
Alternative form of old school.

oldskool
Alternative form of old skool (“hip-hop or rap music of the late 1970s and 1980s (or more recent music of this style) as contrasted with newer styles of such music”) (alternative spelling of old school).

oldtown
Alternative form of old town.

oldtowns
plural of oldtown

oldwife
Alternative form of old wife (“various types of fish”).

oldwives
plural of oldwife

ole
An interjection used to stir up excitement.

olent
scented

oleraceous
Relating to potherbs.

oligistic
Of or relating to oligist, or hematite.

oligoprimer
An oligonucleotide primer

olitory
Of or pertaining to a kitchen garden; used for culinary purposes.

omiletical
Obsolete form of homiletical.

ommateal
Of or pertaining to an ommateum (compound eye).

omniferous
That bears everything; producing all types.

omnifick
Obsolete form of omnific.

omnipotent
Having unlimited power, force or authority.
Describing a cell (especially a stem cell) that is capable of developing into any type of cell or forming any type of tissue (also called a totipotent cell).
Arrant.

omnipotentiary
omnipotent

omnipotents
plural of omnipotent

omnipresential
Omnipresent; present everywhere.

omniscious
Omniscient; all-knowing.

omnivagant
Free-roaming; travelling everywhere.

omphacine
Made from unripe olives.

omphaloptic
biconvex

omy
Mellow, as land.

oncogeriatric
Relating to cancer in elderly patients

ondy
Alternative form of undé.

onelie
Obsolete spelling of only.

onely
Obsolete spelling of only.

onlie
Obsolete spelling of only.

onlies
plural of only

onlucky
Pronunciation spelling of unlucky.

only
Alone in a category.
Singularly superior; the best.
Without sibling; without a sibling of the same gender.
Mere.

onlys
plural of only

onomatopoeial
Of or pertaining to onomatopoeia.

onomatopoeian
A word formed by onomatopoeia.

onomatopoeians
plural of onomatopoeian

onomatopoeious
Of or pertaining to onomatopoeia.

oolitiferous
Bearing oolite.

oosy
Archaic form of oozy.

opacious
Opaque.

opacous
Not shining or illuminated; dark.
Not allowing the passage of light; opaque.

opacular
opaque

operatories
plural of operatory

operatory
effective; practical; operative
Of or relating to operations.

operous
Obsolete form of operose.

opertaneous
Concealed; private.

ophidious
Archaic form of ophidian.

ophiomorphous
Having the form or shape of a snake.

ophiurid
Archaic form of ophiuroid.

ophiurids
plural of ophiurid

ophiurioid
Archaic form of ophiuroid.

ophiurioids
plural of ophiurioid

ophiuroidean
Any brittle star of the class Ophiuroidea

ophthalmick
Obsolete form of ophthalmic.

opime
magnificent, rich, plenteous

opinative
Conjectural; expressing an opinion rather than a fact.
Opinionated, maintaining one's position stubbornly.

opiniastrous
opinionated

opiniative
Archaic form of opinionative.

opiniatre
Obsolete form of opiniaster.

opinionate
To have or express as an opinion; to opine.
To have a given opinion.

opiparous
Sumptuous, luxurious.

opisthobranchiate
Of or pertaining to the Opisthobranchia.

opisthobranchiates
plural of opisthobranchiate

oppilate
To block, to stop up, to obstruct.

oppilative
Obstructive.

oppilatives
plural of oppilative

opplete
full; crowded

opponent
One who opposes another; one who works or takes a position against someone or something; one who attempts to stop the progress of someone or something.
One who opposes another; one who works or takes a position against someone or something; one who attempts to stop the progress of someone or something.
One who opposes another; one who works or takes a position against someone or something; one who attempts to stop the progress of someone or something.
One who opposes another; one who works or takes a position against someone or something; one who attempts to stop the progress of someone or something.
One who opposes another; one who works or takes a position against someone or something; one who attempts to stop the progress of someone or something.

oppugnable
Disputable, contestable, refutable, capable of being oppugned.
Curable, amenable to medical treatment.
Assailable, exposed to enemy's attack.

optable
That may or should be chosen; desirable.

optick
Obsolete form of optic.

optique
Obsolete form of optic.

opuntiaceous
Belonging to the family Opuntiaceae (now mostly subfamily Opuntioideae in Cactaceae).