ob- prefix Etymology: Middle English, from Old French, from Latin, to, toward, against, over, completely, from ob to, before, against, on account of — more at epi- 1.: inward < obimbricate > 2.: incompletely < obrotund > < obround > 3.: in reverse order < obdiplostemonous > 4.: inverse < obovate > < obconic > < obcordate >