1857, "lasting through time," from Greek dia "throughout" (see dia-) + khronos "time" (see chrono-). In linguistics, "concerned with the historical development of a language, historical," by 1927.
Entries linking to diachronic
dia-
before vowels, di-, word-forming element meaning "through, in different directions, between," also often merely intensive, "thoroughly, entirely," from Greek dia "through; throughout," probably cognate with bi- and related to duo "two" (from PIE root *dwo- "two") with a base sense of "twice."
chrono-
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.