late 14c., "deprive of power to injure or terrify, render harmless," a figurative sense, from Old French desarmer (11c.), from des- "reverse of" (see dis-) + armer "to arm" (see arm (v.)). The literal senses "deprive of weapons" (transitive), "put off one's armor or lay down one's weapons" (intransitive) are early 15c. Related: Disarmed; disarming; disarmingly.
updated on August 23, 2018