c. 1300, "a communication transmitted via a messenger, a notice sent through some agency," from Old French message "message, news, tidings, embassy" (11c.), from Medieval Latin missaticum, from Latin missus "a sending away, sending, dispatching; a throwing, hurling," noun use of past participle of mittere "to release, let go; send, throw" (see mission).
The Latin word is glossed in Old English by ærende. Specific religious sense of "divinely inspired communication via a prophet" (1540s) led to transferred sense of "the broad meaning (of something)," which is attested by 1828. To get the message "understand" is by 1960.
"act or fact of sending messages," by 1865, verbal noun from message (v.). Middle English had messagery "the carrying of messages" (late 14c.), from Old French messagerie.
c. 1200, messager (late 12c. as a surname), "one who bears a message; the bearer of a verbal or written communication," from Old French messagier "messenger, envoy, ambassador," from message (see message (n.)). With unetymological -n- inserted by c. 1300 for no apparent reason except that people liked to say it that way (compare passenger, harbinger, scavenger). From c. 1200 as "a harbinger, forerunner, precursor" (in reference to John the Baptist as the precursor of Christ).
Old English ærende "message, mission; answer, news, tidings," from Proto-Germanic *airundija- "message, errand" (source also of Old Saxon arundi, Old Norse erendi, Danish ærinde, Swedish ärende, Old Frisian erende, Old High German arunti "message"), which is of uncertain origin. Compare Old English ar "messenger, servant, herald." Originally of important missions; meaning "short, simple journey and task" is attested by 1640s. Related: Errands. In Old English, ærendgast was "angel," ærendraca was "ambassador."
early 15c., "readiness" (in phrase in prompte), from Latin promptus (see prompt (v.)). Meaning "hint, information suggested, act of prompting" is from 1590s. The computer sense of "message given by a computer requiring or helping the user to respond" is by 1977.