OB- - prefix (also oc- before c, of- before f, op- before p) occurring mainly in words of Latin origin, meaning: 1 exposure, openness (object; obverse).
2 meeting or facing (occasion; obvious).
3 direction (oblong; offer).
4 opposition, hostility, or resistance (obstreperous; opponent; obstinate).
5 hindrance, blocking, or concealment (obese; obstacle; occult).
6 finality or completeness (obsolete; occupy).
7 (in modern technical words) inversely; in a direction or manner contrary to the usual (obconical; obovate). [L f. ob towards, against, in the way of]