diachronic

This term is primarily used in linguistics and sociology to describe an analysis that tracks a subject through time. It focuses on the evolution, development, and historical shifts of a system, treating the subject as a moving target across a chronological axis.

It is the direct opposite of synchronic, which examines a language or phenomenon at a single, frozen point in time without regard for its history. While a synchronic study looks at a snapshot, a diachronic study looks at the entire movie of the subject's existence.