Source: http://www.english-for-students.com/of.html
Timestamp: 2019-04-26 00:07:09+00:00

Document:
Of,ob,oc & op are the root-words for many other words.
These ROOT-WORDS are the Prefixes OB,OC,OF & OP which mean AGAINST & FACING. You will notice that the OB can change to OF, to OC, or even to OP. You guessed it - assimilation. OF before words with f, OC before words with c and OP before words with p. The words with OB are very interesting. In practically every one of them, the thought is opposed to the action.
1.	Obese	:	OB ese (o bese’) adj.
2.	Obituary	:	OB ituary (o bick’ u are e) n.
3.	Object	:	OB ject (ob jekt’) v.
4.	Oppressive	:	OP pressive (o pres’ ive) adj.
5.	Offend	:	OF fend (o fend’) v.
6.	Objurgate	:	OB jurgate (ob’ jur gate) v.
7.	Obligee	:	OB ligee (ob li jee’) n.
8.	Obligate	:	OB ligate (ob’ li gate) v.
9.	Obligatory	:	OB ligatory (o blig’ a tore ee) adj.
10.	Oblige	:	OB lige (o blije’) v.
To bind by a favor or service; force 11.	Oblique	:	OB lique (o bleke’) adj.
12.	Obliquity	:	OB liquity (o blik’ wit ee) n.
13.	Obliterate	:	OB literate (o blit’ e rate) v.
14.	Oblivious	:	OB livious (o bliv’ ee us) adj.
15.	Obloquy	:	OB loquy (ob’ lo kwee) n.
16.	Obscene	:	OB scene (ob sene’) adj.
17.	Oppose	:	OP pose (o poze’) v.
18.	Occlusion	:	OC clusion (o klu’ zhun) n.
19.	Occult	:	OC cult (o kult’) adj.

References: v.

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