Diachronic meaning

dīə-krŏnĭk

Of or concerned with phenomena, such as linguistic features, as they change through time.

adjective

Of or concerned with the study of changes occurring over a period of time, as in language, mores, etc.

adjective

Occurring over or changing with time.

adjective

Of, pertaining to or concerned with changes that occur over time.

adjective

Origin of diachronic

From dia– Greek khronos time

From American Heritage Dictionary of the English Language, 5th Edition
From dia- +‎ chronic.

From Wiktionary