From Latin 'mittere' (to send) via Medieval Latin 'missaticum' — same root as 'mission,' 'missile,' and 'emissary.'
A communication sent from one person or group to another; the central theme or idea of a speech, book, or film; to send a message to someone.
From Old French message (a message, errand, mission), from Medieval Latin missāticum (something sent, a sending), from Latin missus (sent), past participle of mittere (to send, to let go, to release). The word is built on the same past-participial stem as mission (a sending forth), missile (something sent through the air), and emit (to send out). The PIE root behind mittere is debated
The Medieval Latin suffix '-āticum' that formed 'missāticum' (message) was extraordinarily productive in French and generated many common English words. French dropped the unstressed middle syllable, turning '-āticum' into '-age,' which is why English has 'voyage' (from 'viāticum,' provision for a journey), 'passage' (from 'passāticum'), 'damage' (from 'damnāticum'), and 'village' (from 'villāticum').