[1870–75; co- + discoverer]This word is first recorded in the period 1870–75. Other words that entered Englishat around the same time include: Mafia, asymmetric, billing, immobilize, linkageco- 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)