word-forming element meaning "together with, jointly; alike; at the same time," also sometimes completive or intensive, from Greek syn (prep.) "with, together with, along with, in the company of," from PIE *ksun- "with" (source also of Russian so- "with, together," from Old Russian su(n)-). Assimilated to -l-, reduced to sy- before -s- and -z-, and altered to sym- before -b-, -m- and -p-. Since 1970s also with a sense of "synthetic."

before vowels chron-, word-forming element meaning "time," from Latinized form of Greek khronos "time, a defined time, a lifetime, a season, a while," which is of uncertain origin.

"not coinciding in time," 1735, from a- (3) "not, without" + synchronous "existing or happening at the same time." Related: Asynchronicity; asynchronism (1850).

"occurring at the same time," 1775, shortening of synchronical (1650s), from Late Latin synchronus "simultaneous" (see synchronous). Linguistic sense is first recorded 1922, probably a borrowing from French synchronique (de Saussure, 1913). Synchronal "simultaneous" is from 1650s. Related: synchronically.

1580s, "quality of being synchronous," from Modern Latin synchronismus, from Greek synkhronismos, from synkhronos (see synchronous). Meaning "recurring at the same successive instants of time" is from 1854.

1620s, "to occur at the same time," from Greek synkhronizein "be of the same time," from synkhronos "happening at the same time" (see synchronous). The transitive sense of "make synchronous" is first recorded 1806. Of timepieces by 1879. Related: Synchronized; synchronizing. Synchronized swimming is recorded from 1950.

"occurrence or existence at the same time," 1848, from Greek synkhronos (see synchronous) + -y (2).