early 13c., "alteration;" mid-14c., "action of substituting one thing for another;" verbal noun from change (v.). Changing-room is from 1917.
early 14c., "one who alters the form of anything," agent noun from change (v.), or else from Old French changeour "money-changer, barterer," from changier. Meaning "money-changer" in English is from mid-14c. Meaning "mechanism for automatically changing records on a record-player" is from 1930.
1550s, "one given to change," from change (n.) + diminutive suffix -ling. Meaning "person or thing left in place of one secretly taken" is from 1560s; specific reference to an infant or young child (usually stupid, strange, or ugly) superstitiously believed to have been left by the faeries in place of a beautiful or charming one they have stolen away is from 1580s. An earlier word for it was oaf or auf.
phrase expressing the fundamental immutability of life, human situations, etc., 1903, French, plus ça change, plus c'est la même chose (1849), literally "the more it changes, the more it stays the same."
late 14c., eschaunge, "act of reciprocal giving and receiving," from Anglo-French eschaunge, Old French eschange (Modern French échange), from Late Latin excambium, from excambiare, from Latin ex "out" (see ex-) + cambire "barter" (see change (v.)). The practice of merchants or lenders meeting at certain places to exchange bills of debt led to the meaning "building for mercantile business" (1580s).
1680s (in hump-backed), of uncertain origin; perhaps from Dutch homp "lump," from Middle Low German hump "bump," from Proto-Germanic *hump-, from PIE *kemb- "to bend, turn, change, exchange" (see change (v.)). Replaced, or perhaps influenced by, crump, from Old English crump.
A meaning attested from 1901 is "mound in a railway yard over which cars must be pushed," which might be behind the figurative sense of "critical point of an undertaking" (1914). By 1957, hump day was in use in reference to the mid-point of a training program or course; it was extended to "Wednesday," as the mid-point of the work-week, by 1987.
late 14c., permuten, "to change one for another, to interchange," from Old French permuter and directly from Latin permutare "to change thoroughly," from per "thoroughly" (see per) + mutare "to change" (from PIE root *mei- (1) "to change, go, move"). The mathematical sense is from 1878 (see permutation).