1765, "to extend or get beyond the flank" (of an opposing army), from out- + flank (v.). Figurative use, get the better of, outmaneuver," is from 1773. Related: Outflanked; outflanking.
outermost
outerwear
outface
outfield
outfit
outflank
outflow
outfox
outgoing
outgrow
outgrowth