Wiktionary
diachrony
n. The study of change over time, especially changes to language
Usage examples of "diachrony".
It was a violence, a terrible intrusion in the succession of moments, a clot in diachrony, and with the dumb arrogance of its existence it paid the outrage of ontology no mind.
The source of pressure is narrative, in that if any Oriental detail can be shown to move, or to develop, diachrony is introduced into the system.
The second, which replaces synchrony by diachrony, is more productive, but sins by being too teleological.