ob-

(also oc- before c; of- before f; op- before p)

prefix forming words of mainly Latin origin, meaning:

1》 to, towards: obverse.

2》 against; blocking: opponent.

    ↘concealment: occult.

3》 finality or completeness: obsolete.

4》 technical in a direction or manner contrary to the usual: obconical.

Origin

from L. ob 'towards, against, in the way of'.