Diachronicity refers to the temporal and historical aspects of language or culture. Alternatives to this word include "historicity," "temporality," "chronicity," and "temporal dynamics." Additionally, "evolutionary progression" and "time-dependent change" can also be used to express the concept of diachronicity. These synonyms are important for describing how language and culture evolve over time and how certain linguistic or cultural aspects develop and change. By using these words, one can effectively convey temporal aspects of a language or culture and provide insight into how it has evolved over the course of history.