early 15c., "a combination for some purpose, cooperation" (a sense now archaic or obsolete), from Old French concurrence (14c.) or directly from Medieval Latin concurrentia "a running together," from concurrens, present participle of concurrere "to run together, assemble hurriedly; clash, fight," in transferred use, "to happen at the same time," from assimilated form of com "together" (see con-) + currere "to run" (from PIE root *kers- "to run").

The sense of "occurrence together in time, coincidence" is from c. 1600. The meaning "accordance in opinion" is by 1660s.

late 14c., "acting in conjunction, contributing to the same effect or event," from Old French concurrent or directly from Latin concurrentem (nominative concurrens), present participle of concurrere "run together, assemble hurriedly; clash, fight," in transferred use, "happen at the same time" (see concur). Related: Concurrency; concurrently.

The meaning "running together side by side" is from late 15c. The meaning "combined, joint" is by 1530s. In law, concurrent jurisdiction (that possessed equally by two courts and if exercised by one not usually assumed by the other) is recorded from 1767.

1580s, "quality of being synchronous, contemporary existence or occurrence, concurrence of two or more events in time," from Modern Latin synchronismus, from Greek synkhronismos, from synkhronos (see synchronous). The meaning "quality of recurring at the same successive instants of time" is from 1854.

"a number of symptoms occurring together," 1540s, from medical Latin, from Greek syndrome "concurrence of symptoms, concourse of people," from syndromos "place where several roads meet," literally "a running together," from syn- "with" (see syn-) + dromos "a running, course" (see dromedary).

Phrase _____ syndrome, indicating a characteristic complex of beliefs, behaviors, etc., is by 1955, from psychology.

c. 1300, accordaunce, "compliance;" early 14c., "agreement, concurrence, state of being in accord," from Old French acordance "agreeing, reconciliation, harmony," noun of action from acorder "reconcile, agree, be in harmony" (see accord (v.)).

Of things, "conformity, compatibility, harmony," late 14c. The meaning "formal adjustment of a difference, peace treaty" is from late 13c. Phrase in accordance with is attested by 1793 (in Middle English, in accordance of was the usual form).

c. 1600, "exact correspondence in substance or nature," from French coincidence, from coincider, from Medieval Latin coincidere, literally "to fall upon together," from assimilated form of Latin com "with, together" (see com-) + incidere "to fall upon" (from in- "upon" + combining form of cadere "to fall," from PIE root *kad- "to fall").

From 1640s as "occurrence or existence during the same time." Meaning "a concurrence of events with no apparent connection, accidental or incidental agreement" is from 1680s, perhaps first in writings of Thomas Browne.

Old English, from Late Latin amen, from Ecclesiastical Greek amen, from Hebrew amen "truth," used adverbially as an expression of agreement (as in Deuteronomy xxvii.26, I Kings i.36), from Semitic root a-m-n "to be trustworthy, confirm, support."

Compare similar use of Modern English certainly, absolutely. Used in Old English only at the end of Gospels, otherwise translated as Soðlic! or Swa hit ys, or Sy! As an expression of concurrence after prayers, it is recorded from early 13c. Amen corner is attested from 1860.

1840, "concurrence, coincidence," literally "a jumping together," formed on model of resilience from Latin consilient-, from assimilated form of com "with, together" (see con-) + salire "to leap" (see salient (adj.)).