1760, "to free (a gun) from its limber," usually for the purpose of bringing it into action, from un- (2) "opposite of" + limber "attach a gun to its limber" (see limber (n.)). Figurative sense is attested from 1864. Related: Unlimbered; unlimbering.
unless
unlettered
unlicensed
unlike
unlikely
unlimber
unlimited
unlink
unlisted
unlivable
unload