WordNet sense 1 (used of the study of a phenomenon (especially language) as it changes through time):

diachronic

WordNet sense 2 (being or occurring in fact or actuality; having verified existence; not illusory):

existent, real, real, real

WordNet sense 3 (belonging to the past; of what is important or famous in the past):

historic

WordNet sense 4 (earlier than the present time; no longer current):

past