adaptation (n.)

c. 1600, "action of adapting (something to something else)," from French adaptation, from Late Latin adaptationem (nominative adaptatio), noun of action from past-participle stem of adaptare "to adjust," from ad "to" (see ad-) + aptare "to join," from aptus "fitted" (see apt).

Meaning "condition of being adapted, state of being fitted to circumstances or relations" is from 1670s. Sense of "modification of a thing to suit new conditions" is from 1790. Biological sense "variations in a living thing to suit changed conditions" first recorded 1859 in Darwin's writings.