diachronic
adjective
ˌdaɪəˈkrɒnɪk 
ˌdaɪəˈkrɑːnɪk relating to the way something, especially a language, has developed over time
compare synchronic
Definition of diachronic adjective from the Oxford Advanced Learner's Dictionary
ˌdaɪəˈkrɒnɪk ˌdaɪəˈkrɑːnɪk 