Definitions for diachronicˌdaɪ əˈkrɒn ɪk
Random House Webster's College Dictionary
di•a•chron•icˌdaɪ əˈkrɒn ɪk(adj.)
of or pertaining to the study of the changes in a language over a period of time: diachronic linguistics.
Ref: Compare synchronic.
Origin of diachronic:
1925–30; < F diachronique (F. de Saussure); see dia -, chronic
used of the study of a phenomenon (especially language) as it changes through time
Occurring or changing along with time.