adventitious (adj.)

"of the nature of an addition from without, not from the essence of the subject; accidentally or casually acquired," c. 1600, from Medieval Latin adventitius "coming from abroad, extraneous," a corruption of Latin adventicius "foreign, strange, accidental," from advent- past participle stem of advenire "to arrive at, reach, come to" (see advent). Related: Adventitiously; adventitiousness.