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CO

1. Colorado (approved esp. for use with zip code).
2. Commanding Officer.
3. conscientious objector.

Co

—Symbol, Chem.
cobalt.

co-

var. of com- before a vowel, h, and gn: coadjutor; cohabit; cognate. The prefix co- now productively forms new words from bases beginning with any sound (co-conspirator; co-manage; coseismic), sometimes with the derived sense “auxiliary, subsidiary” (coenzyme; copilot), and, in mathematics and astronomy, with the sense “complement” (codeclination).