1520s, from Late Latin imperativus "pertaining to a command," from imperatus "commanded," past participle of imperare "to command, to requisition," from assimilated form of in- "into, in" (see in-(2)) + parare "prepare" (see pare).

mid-15c., in grammar; later "something imperative" (c.1600), from Old French imperatif and directly from Late Latin imperativus (see imperative, adj.).