Ob.

A Latin preposition, signifying, primarily, in front, before, and hence against, toward, as in ob-jicere, to object, i. e., to throw against. It means reversed or back, in obovate, occiput, &c., and often on or in. In composition, the letter b is often changed into the first letter of the word to which it is prefixed, as in occasion, offer, oppose.