Yours, Etc.: Origins and Uses of 8 Sign-Offs
early 15c., "to throw or cast down," from Old French dejeter (12c.), from Latin deiectus "a throwing down, felling, fall," past participle of deicere "to cast down, destroy; drive out; kill, slay, defeat," from de- "down" + -icere, comb. form of iacere "to throw" (see jet (v.)). Originally literal; the sense of "depress in spirit" is c.1500.