of-

Multiple Entries:
  of-    ob-  

Concise Oxford English Dictionary © 2008 Oxford University Press:
of-/ɒf/

▶prefix variant spelling of ob-. assimilated before f (as in offend).

Concise Oxford English Dictionary © 2008 Oxford University Press:
ob- /ɒb/ (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’.