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• Co
  Co

  cobalt.
• CO
  CO

  abbreviation

  Colorado (approved especially for use with zip code).
• Co.
  Co.

  abbreviation

  Company.
• c/o
  c/o

  care of.
• C/o
  C/o

  care of.
• C/O
  C/O

  cash order.
• co-
  co-

  variant 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 ).
• c.o.
  c.o.

  abbreviation

  care of.
• C.O.
  C.O.

  abbreviation

  cash order.
• co
  co

  abbreviation

  a commercial company (used with a country domain name)

Co

¹ American  

Symbol, Chemistry.

1. cobalt.

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CO ² American  

abbreviation

1. Colorado (approved especially for use with zip code).

2. commanding officer.

3. conscientious objector.

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Co. ³ American  

Or co.

abbreviation

1. Company.

2. County.

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c/o ⁴ American  

1. care of.

2. Bookkeeping. carried over.

3. cash order.

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C/o ⁵ American  

1. care of.

2. Bookkeeping. carried over.

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C/O ⁶ American  

1. cash order.

2. certificate of origin.

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co- ⁷ American  

1. variant 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 ).

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c.o. ⁸ American  

abbreviation

1. care of.

2. carried over.

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C.O. ⁹ American  

abbreviation

1. cash order.

2. Commanding Officer.

3. conscientious objector.

4. correction officer.

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CO ¹ British  

abbreviation

1. Commanding Officer

2. Commonwealth Office

3. conscientious objector

4. Colorado

5. Colombia (international car registration)

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co- ² British  

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

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Co ³ British  

abbreviation

1. (esp in names of business organizations) Company

2. informal and the rest of them

   Harold and co

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c/o ⁴ British  

abbreviation

1. care of

2. accounting carried over

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co ⁵ British  

abbreviation

1. a commercial company (used with a country domain name)

2. Colombia

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Co ⁶ British  

symbol

1. cobalt

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Co ⁷ British  

abbreviation

1. County

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Etymology

Origin of co-

from Latin, reduced form of _com-

Example Sentences

The co- leader of Aberdeen City Council, Ian Yuill, told BBC Scotland News it had been the most intense and sustained period of snow he could remember in more than 50 years.

From BBC • Jan. 6, 2026

“Happy Father’s Day to my baby daddy and rad co- parent,” she captioned a pair of family photos.

From Los Angeles Times • Nov. 4, 2025

He added, "We are committed to advancing our efforts to transform the prospect of a universal treatment, capable of controlling co- and serial infections of respiratory viruses and bacteria, into a reality."

From Science Daily • Mar. 18, 2024

“The Yamnaya are extraordinary,” says the study’s co- author Volker Heyd, an archaeologist at the University of Helsinki.

From Scientific American • Mar. 3, 2023

NOTE.—The forms co-, col-, com-, and cor-, are euphonic variations of con-.

From New Word-Analysis by William Swinton