ob-

  1. a prefix meaning “toward,” “to,” “on,” “over,” “against,” originally occurring in loanwords from Latin, but now used also, with the sense of “reversely,” “inversely,” to form Neo-Latin and English scientific terms: object; obligate; oblanceolate.
Also o- oc-, of-, op-.

Origin of ob-

Middle English (< Old French) < Latin, representing ob (preposition); in some scientific terms, < New Latin, Latin ob-
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British Dictionary definitions for ob-

ob-

prefix
  1. inverse or inverselyobovate

Word Origin for ob-

from Old French, from Latin ob. In compound words of Latin origin, ob- (and oc-, of-, op-) indicates: to, towards (object); against (oppose); away from (obsolete); before (obstetric); down, over (obtect); for the sake of (obsecrate); and is used as an intensifier (oblong)
Collins English Dictionary - Complete & Unabridged 2012 Digital Edition © William Collins Sons & Co. Ltd. 1979, 1986 © HarperCollins Publishers 1998, 2000, 2003, 2005, 2006, 2007, 2009, 2012

Word Origin and History for ob-

prefix meaning "toward, against, across, down," also used as an intensive, from Latin ob "toward, to, over against, in the way of, by reason of, about, before, in front of," from PIE root *epi, also *opi "near, against" (see epi-).

Online Etymology Dictionary, © 2010 Douglas Harper