c. 1200, "to alter, make different, change" (transitive); early 13c. as "to substitute one for another;" mid-13c. as "to make (something) other than what it was, cause to turn or pass from one state to another;" from late 13c. as "to become different, be altered" (intransitive), from Old French changier "to change, alter; exchange, switch," from Late Latin cambiare "to barter, exchange," extended form of Latin cambire "to exchange, barter," a word of Celtic origin, from PIE root *kemb- "to bend, crook" (with a sense evolution perhaps from "to turn" to "to change," to "to barter"); cognate with Old Irish camm "crooked, curved;" Middle Irish cimb "tribute," cimbid "prisoner;" see cant (n.2).
From c. 1300 as "undergo alteration, become different." In part an abbreviation of exchange. From late 14c. especially "to give an equivalent for in smaller parts of the same kind" (money). Meaning "to take off clothes and put on other ones" is from late 15c. Related: Changed;changing. To change (one's) mind is from 1590s.
Old English be- (unstressed) or bi (stressed) "near, in, by, during, about," from Proto-Germanic *bi "around, about," in compounds often merely intensive (source also of Old Saxon and Old Frisian bi "by, near," Middle Dutch bie, Dutch bij, German bei "by, at, near," Gothic bi "about"), from PIE *bhi, reduced form of root *ambhi- "around."
As an adverb by c. 1300, "near, close at hand." OED (2nd ed. print) has 38 distinct definitions of it as a preposition. Originally an adverbial particle of place, which sense survives in place names (Whitby, Grimsby, etc., also compare rudesby). Elliptical use for "secondary course" was in Old English (opposed to main, as in byway, also compare by-blow "illegitimate child," 1590s, Middle English loteby "a concubine," from obsolete lote "to lurk, lie hidden"). This also is the sense of the second by in the phrase by the by (1610s). By the way literally means "along the way" (c. 1200), hence "in passing by," used figuratively to introduce a tangential observation ("incidentally") by 1540s.
To swear by something or someone is in Old English, perhaps originally "in the presence of." Phrase by and by (early 14c.) originally meant "one by one," with by apparently denoting succession; modern sense of "before long" is from 1520s. By and large "in all its length and breadth" (1660s) originally was nautical, "sailing to the wind and off it," hence "in one direction then another;" from nautical expression large wind, one that crosses the ship's line in a favorable direction.
c. 1200, "act or fact of changing," from Anglo-French chaunge, Old French change "exchange, recompense, reciprocation," from changier "to alter; exchange; to switch" (see change (v.)). Related: changes.
Meaning "a different situation, variety, novelty" is from 1680s (as in for a change, 1690s). Meaning "something substituted for something else" is from 1590s. Meaning "place where merchants meet to do business" is from c. 1400. Meaning "the passing from life to death" is biblical (161os).
The financial sense of "balance of money returned after deducting the price of a purchase from the sum paid" is first recorded 1620s; hence to make change (by 1865). Bell-ringing sense is from 1610s, "any sequence other than the diatonic." Hence the figurative phrase ring changes "repeat in every possible order" (1610s). Figurative phrase change of heart is from 1828. In reference to women, change of life "final cessation of menstruation" is recorded from 1834.