mid-15c., "covered walk or passageway, narrow and partly open passageway along a wall," from Old French galerie "a long portico" (14c.), from Medieval Latin galeria, of unknown origin. Perhaps an alteration of galilea "church porch," which is probably from Latin Galilaea "Galilee," the northernmost region of Palestine (see Galilee); church porches sometimes were so called, perhaps from being at the far end of the church:
Super altare Beatæ Mariæ in occidentali porte ejusdem ecclesiæ quæ Galilæ a vocatur. [c.1186 charter in "Durham Cathedral"]
Sense of "building to house art" first recorded 1590s. In reference to theaters, of the section with the highest, cheapest seats; hence "people who occupy a (theater) gallery" (contrasted with "gentlemen of the pit") first by Lovelace, 1640s, hence to play to the gallery (1867).
By normal evolution the Modern English form would be *gatelope, but the current spelling (first attested 1660s, not fixed until mid-19c.) is from influence of gauntlet (n.1) "a glove," "there being some vague association with 'throwing down the gauntlet' in challenge" [Century Dictionary].
"temporary passageway" to a ship, building under construction, etc., ultimately from Old English gangweg "road, passage, thoroughfare;" a compound of gang (n.) in its original sense "a going, journey, way, passage" and way (n.). Nautical use dates from 1680s in reference to a passage on the ship, from 1780 of the opening at the side whereby people enter and leave, and by 1840s of the board or bridge they use to get to and from the dock. As a command to clear way, attested by 1912, American English. In British parliamentary use, with somewhat the same sense aisle has in the U.S. Congress.
Below the g[angway], as a parliamentary phrase, is applied to members whose customary seat does not imply close association with the official policy of the party on whose side of the House they sit. [Fowler]
Old English paþ, pæþ "narrow passageway or route across land, a track worn by the feet of people or animals treading it," from West Germanic *patha- (source also of Old Frisian path, Middle Dutch pat, Dutch pad, Old High German pfad, German Pfad "path"), a word of uncertain origin, not attested in Old Norse or Gothic.
The original initial -p- in a Germanic word is an etymological puzzle. Don Ringe ("From Proto-Indo-European to Proto-Germanic," Oxford 2006), reflecting an old theory, describes it as "An obvious loan from Iranian ..., clearly borrowed after Grimm's Law had run its course." Watkins says the word is "probably borrowed (? via Scythian) from Iranian *path-," from PIE root *pent- "to tread, go, pass" (source of Avestan patha "way;" see find (v.)), but this is too much of a stretch for OED and others. In Scotland and Northern England, commonly a steep ascent of a hill or in a road.
early 14c., "bed of a stream of water," from Old French chanel "bed of a waterway; tube, pipe, gutter," from Latin canalis "groove, channel, waterpipe" (see canal). Given a broader, figurative sense by 1530s: "that by which something passes or is transmitted" (of information, commerce, etc.); meaning "circuit for telegraph communication" (1848) probably led to that of "band of frequency for radio or TV signals" (1928).
Also "part of a sea making a passageway between land masses, a large strait" (1550s). English Channel is from 1825; the older name was British Channel (by 1730) or simply Channel (Shakespeare). John of Trevisa's Middle English translation of the encyclopedia De Proprietatibus Rerum (c. 1398) has frensshe see for "English Channel." The Channel Islands are the French Îles Anglo-Normandes.