Etymology
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passenger (n.)

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 The oldest sense now is obsolete; meaning "one traveling in a public vehicle or vessel," especially in exchange for a fare, is attested from 1510s; hence, in modern use, "one riding in a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.

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passer-by (n.)
also passerby, 1560s, from agent noun of pass (v.) + by; earlier, this sense was in passager (see passenger).
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messenger (n.)

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).

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porringer (n.)

"a porridge-dish; a small vessel deeper than a plate, usually with upright sides, a nearly flat bottom, and one or two ears," late 15c., alteration of potynger, potager "small dish for stew," from Middle English potage (see pottage) by the same course of changes that produced porridge; and with unetymological -n- by 1530s (compare passenger).

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*pete- 
*petə-, Proto-Indo-European root meaning "to spread."

It forms all or part of: compass; El Paso; expand; expanse; expansion; expansive; fathom; pace (n.); paella; pan (n.); pandiculation; pas; pass; passe; passim; passacaglia; passage; passenger; passport; paten; patent; patina; petal; spandrel; spawn.

It is the hypothetical source of/evidence for its existence is provided by: Greek petannynai "to spread out," petalon "a leaf," patane "plate, dish;" Old Norse faðmr "embrace, bosom," Old English fæðm "embrace, bosom, fathom," Old Saxon fathmos "the outstretched arms."
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scavenger (n.)

1540s, originally "person hired to remove refuse from streets," a modification of Middle English scavager, scawageour (late 14c.), the title of a London official who originally was charged with collecting tax on goods sold by foreign merchants.

This is from Middle English scavage, scauage (Anglo-French scawage) "toll or duty exacted by a local official on goods offered for sale in one's precinct" (c. 1400), from Old North French escauwage "inspection," from a Germanic source (compare Old High German scouwon, Old English sceawian "to look at, inspect;" see show (v.)).

The scavenger later was charged with inspection and maintenance of streets: Blount's description ("Glossographia," 1656) is "an Officer well known in London, that makes clean the streets, by scraping up and carrying away the dust and durt." The modern general sense of the word "one who collects and consumes or puts to use what has been discarded" evolved through the notion of "collect and dispose of rubbish."

The word came to be regarded as an agent noun in -er, but the verb scavenge (q.v.) is a late back-formation from the noun. For the unetymological -n- (c. 1500), compare harbinger, passenger, messenger, etc. Extended 1590s to animals that feed on decaying matter. Scavenger hunt is attested from 1937. Mayhew (1851) has scavagery "street-cleaning, removal of filth from streets."

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street-car (n.)
"passenger car for city travel," horse-drawn at first, later cable-powered, 1859, American English, from street (n.) + car (n.).
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titanic (adj.)
"gigantic, colossal," 1709, from titan + -ic. The British passenger liner R.M.S. Titanic sank April 15, 1912, and the name became symbolic of the destruction of supposedly indestructible.
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Concorde (n.)

supersonic passenger airliner operating from 1976 to 2003, from French concorde, literally "harmony, agreement" (see concord (n.)), reflecting the Anglo-French collaborative agreement that produced it.

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stewardess (n.)
1630s, "female steward," from steward (n.) + -ess. Meaning "female attendant on passenger aircraft" is from 1931; used of ships (where she waited on the female passengers) from 1837.
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