mid-14c., "inclined, disposed;" late 14c., "suited, fitted, adapted," from Old French ate (13c., Modern French apte), or directly from Latin aptus "fit, suited," adjectival use of past participle of *apere "to attach, join, tie to," from PIE root *ap- (1) "to grasp, take, reach" (cognates: Sanskrit apnoti "he reaches," Latin apisci "to reach after, attain," Hittite epmi "I seize"). Elliptical sense of "becoming, appropriate" is from 1560s.