1630s, "outlying land of a farm" (especially in Scotland), from out- + field (n.); sporting sense is attested from 1851 in cricket, 1868 in baseball, "part of the field most remote from the batsman/batter." Related: Outfielder.
outen
outer
outermost
outerwear
outface
outfield
outfit
outflank
outflow
outfox
outgoing