diachrony
noun
di·ach·ro·ny dī-ˈa-krə-nē 
1
: diachronic analysis
2
: change extending through time
Word History
Etymology
borrowed from French diachronie, from dia- dia- + Greek chrónos "time, duration" (of obscure origin) + French -ie -y entry 2
Note: Term introduced, along with the adjective diachronique, by Ferdinand de saussure in the posthumously published Cours de linguistigue générale (Lausanne/Paris, 1916), compiled from lecture notes by his students. See also synchronic, synchrony.
First Known Use
circa 1939, in the meaning defined at sense 1