also co-operate, "to act or operate jointly with another or others to the same end," c. 1600, from Late Latin cooperatus, past participle of cooperari "to work together with," from assimilated form of com "with, together" (see com-) + operari "to work," from PIE root *op- "to work, produce in abundance." Cooperator "fellow worker, associate" is attested from early 15c. Related: Cooperated; cooperating.
