messenger n.

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.

mid-14c., passager "a passer-by; a traveler," from Old French passagier, passageor "traveler, passer-by" (Modern French passager), noun use of passagier (adj.) "passing, fleeting, traveling," from passage "mountain pass, passage" (11c.), from passer "to go by," from Vulgar Latin *passare "to step, walk, pass," from Latin passus "step, pace" (from PIE root *pete- "to spread").

And in this I resemble the Lappwing, who fearing hir young ones to be destroyed by passengers, flyeth with a false cry farre from their nestes, making those that looke for them seeke where they are not .... [John Lyly, "Euphues and His England," 1580]

The -n- was added early 15c. (compare messenger, harbinger, scavenger, porringer). The oldest sense now is obsolete; meaning "one traveling in a public vehicle or vessel," especially in exchange for a fare, is attested from 1510s; hence, in modern use, "one riding in a private vehicle driven by another." The railroad passenger-car is attested from 1832. The North American passenger-pigeon was so called from 1802 for its extensive wanderings in search of food; they have been extinct since 1914.