[1590–1600; co- + agent]This word is first recorded in the period 1590–1600. Other words that entered Englishat around the same time include: Byzantine, radius, tea, tube, volunteerco- is a prefix meaning “with,” “together,” “in association,” sometimes with the derivedsense “auxiliary, subsidiary” (coenzyme; copilot), and, in mathematics and astronomy, with the sense “complement” (codeclination)