1650s, "to select (someone) for a group or club by a vote of members," from L. cooptare "to choose as a colleague or member of one's tribe," from com- "together" + optare "choose" (see option). For some reason this defied the usual pattern of L.-to-Eng. adaptation, which
should have yielded cooptate. Sense of "take over" is first recorded c.1953. Related: co-opted (1650s).