"agreement between things, harmony," late 14c., from Old French congruité "relevance, appropriateness" or directly from Late Latin congruitatem (nominative congruens) "agreement," from congruus "suitable, agreeing," from congruere "to agree, correspond with," literally "to come together," from assimilated form of com "with, together" (see con-) + a lost verb *gruere, *ruere "fall, rush" (see congruent).

1828, "sacred choral song; musical composition in harmony, suited for performance by a choir," from German Choral "metrical hymn in Reformed church," shortened from Choralgesang "choral song," translating Medieval Latin cantus choralis, from Latin choralis "belonging to a chorus or choir," from chorus (see chorus). The -e was added to indicate stress. Meaning "group of singers performing choral music" is from 1942.

mid-15c., "a harmony of the Gospels;" 1620s, "action of fusing together," from Late Latin conflationem (nominative conflatio), noun of action from past-participle stem of Latin conflare "bring together, compose," also "melt together," literally "to blow together," from assimilated form of com "with, together" (see con-) + flare "to blow" (from PIE root *bhle- "to blow"). Meaning "inadvertent combination of two readings of the same passage" is from 1881.

"oboe, double-reeded woodwind instrument," 1570s, from French hautbois "high wood" (15c.; see oboe, which is the Italian phonetic spelling of the French word). The haut is used here in its secondary sense of "high-pitched." In early use frequently nativized as hoboy, hawboy, etc.

This Pageaunt waz clozd vp with a delectable harmony of Hautboiz, Shalmz, Coronets, and such oother looud muzik. [Robert Laneham, 1575]

"small, keyed, bellows-like wind instrument," 1830, from German Akkordion, from Akkord "musical chord, concord of sounds," from a verb similar to Old French acorder "agree, be in harmony," from Vulgar Latin *accordare (compare Italian accordare "to attune a musical instrument;" see accord (v.)), with suffix on analogy of clarion, etc. Invented 1829 by piano-maker Cyrill Demian of Vienna. The type with a keyboard instead of buttons is a piano accordion. Related: Accordionist.

1560s, "a chafing, rubbing," from French friction (16c.) and directly from Latin frictionem (nominative frictio) "a rubbing, rubbing down," noun of action from past-participle stem of fricare "to rub, rub down," which is of uncertain origin. Watkins suggests possibly from PIE root *bhreie- "to rub, break." De Vaan suggests a PIE bhriH-o- "to cut" and compares Sanskrit bhrinanti, Old Church Slavonic briti "to shave." Sense of "resistance to motion" is from 1722; figurative sense of "disagreement, clash, lack of harmony, mutual irritation" first recorded 1761. Related: Frictional.

1660s, "agreement of two or more in design or plan; accord, harmony," from French concert (16c.), from Italian concerto "concert, harmony," from concertare "bring into agreement," apparently from Latin concertare "to contend with zealously, contest, dispute, debate" from assimilated form of com "with" (see con-) + certare "to contend, strive," frequentative of certus, variant past participle of cernere "separate, distinguish, decide" (from PIE root *krei- "to sieve," thus "discriminate, distinguish").

The proposed sense evolution between Latin ("to contend with") and medieval Italian  ("bring into agreement") seems extreme and is difficult to explain. Perhaps the shift is from "to strive against" to "to strive alongside" (compare English fight with), or perhaps it is via the notion of "confer, arrange by conference, debate for the sake of agreement." Some have suggested the sense shifted through confusion of Latin concertus with consertus, past participle of concerere "to join, fit, unite."

Sense of "public musical performance," usually of a series of separate pieces, is from 1680s, from Italian (Klein suggests Latin concentare "to sing together," from con- + cantare "to sing," as the source of the Italian word in the musical sense). The general sense of "any harmonious agreement or orderly union" is from 1796. Concert-master "first violinist of an orchestra" is from 1815, translating German Konzertmeister.

1590s, "firmness of matter," from Medieval Latin consistentia   literally "a standing together," or directly from Latin consistentem (nominative consistens), present participle of consistere "to stand firm, take a standing position, stop, halt," from assimilated form of com "with, together" (see con-) + sistere "to place," causative of stare "to stand, be standing," from PIE root *sta- "to stand, make or be firm."

Meaning "state of being in agreement or harmony" (with something) is from 1650s; meaning "steady adherence to principles, patterns of action, etc." is from 1716. Meaning "harmonious connection, as of the parts of a system" is from 1787.