co-

UK: /ˈkəʊ-/

Collins Concise English Dictionary © HarperCollins Publishers::

co- prefix

1. together; joint or jointly; mutual or mutually: coproduction
2. indicating partnership or equality: cofounder, copilot
3. to the same or a similar degree: coextend
4. (in mathematics and astronomy) of the complement of an angle: cosecant, codeclination

Etymology: from Latin, reduced form of com-

WordReference Random House Learner's Dictionary of American English © 2025

CO,  an abbreviation of:

1. Place Names Colorado.
2. Military Commanding Officer.
3. conscientious objector.

co-, prefix. 

1. co- comes from Latin, where it has the meaning "joint, jointly, together.'' This meaning is found in such words as: costar, coworker.
2. A similar meaning for this prefix is "auxiliary, helping.'' This meaning is found in such words as: copilot.

Co. or co., an abbreviation of:

1. Company.
2. County.

C/o or c/o, an abbreviation of:

1. care of.

c.o.,  an abbreviation of:

1. care of.
2. carried over.

WordReference Random House Unabridged Dictionary of American English © 2025

CO, 

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

Co, [Symbol, Chem.]

1. Chemistry cobalt.

co-, 

1. 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).

Co., 

1. Company.
2. County.
Also, co. 

C/O, 

1. Business cash order.
2. certificate of origin.

C/o, 

1. care of.
2. Business [Bookkeeping.] carried over.

c/o, 

1. care of.
2. Business [Bookkeeping.] carried over.
3. Business cash order.

C.O., 

1. Business cash order.
2. Military, Commanding Officer.
3. conscientious objector.
4. correction officer.

c.o., 

1. care of.
2. carried over.