apt adj.

early 15c. (implied in adapted) "to fit (something, for some purpose)," from Old French adapter (14c.), from Latin adaptare "adjust, fit to," from ad "to" (see ad-) + aptare "to join," from aptus "fitted" (see apt). Intransitive meaning "to undergo modification so as to fit new circumstances" is from 1956. Related: Adapting.

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).

The meaning "condition of being adapted, state of being fitted to circumstances or relations" is from 1670s. The sense of "modification of a thing to suit new conditions" is from 1790. The biological sense of "variations in a living thing to suit changed conditions" is by 1859, in Darwin's writings.