co-

From Latin co-, allomorph of Latin con-.

• enPR: kōʹ
  • (Received Pronunciation) IPA^(key): /ˈkəʊ-/, /ˌkəʊ-/
  • (General American, Canada) IPA^(key): /ˈkoʊ-/, /ˌkoʊ-/
  • (Indic) IPA^(key): /koː/, /ko/
  • (Inland Northern American) IPA^(key): /ˈkoʊ-/, [ˈkʌo-], /ˌkoʊ-/, [ˌkʌo-]

    • Audio (Milwaukee, Wisconsin):

      (file)

  • (General Australian) IPA^(key): /ˈkəʉ-/, /ˌkəʉ-/
  • (New Zealand) IPA^(key): /ˈkɐʉ-/, /ˌkɐʉ-/
• (unstressed form) enPR: kŏ, IPA^(key): /kɒ-/

co-

2. Together: the root word is done co-incidently.
   2. Jointly: the root verb is done in coordination between multiple actors or entities

      coadoption is joint adoption, coadapt is to adapt together, coanalysis is analysis together

   4. Along with: the root verb is done along with or in addition to others.

      coassemble is to assemble along with others, coadhesion is adhesion along with another material, coadsorb is to be adsorbed along with another substance. Here there is not an indication of intentional coordination.

   6. Mutually: the root is done in a way that is reciprocal and bidirectional.

      coadherence is mutual adherence, coattraction is mutual attraction, coannihilate is to annihilate each other. Unlike the sense of jointly where it is done by both, this sense indicates it is being both to each other.

   8. Simultaneously, done or able to do at the same time.

      cobirthing is simultaneous bringing into being, cosexual is being able to simultaneously reproduce as both female and male, cocluster is a simultaneous cluster of rows and columns, coagglutination is the simultaneous agglutination of two or more proteins or antigens. This sense emphasizes the temporal aspect.

   10. Spatially located or positioned together, co-located.

       cocirculate is to circulate together, coarctate is arctated together, coattend is to attend together.

   12. In conjunction: the root needs another entity to take effect, or there is a one-way interaction between them.

       coantioxidant is a material that has antioxidant activity in the presence of another, codepletion is the depletion of one substance in conjunction with the depletion of another, comedication is a second medication used to alleviate the side-effects of another

   14. Moving or oriented in the same direction; co-directional.

       coflowing is flowing in the same direction, cocurrent is of or pertaining to flow in the same direction, coalign is to align together

   16. Gender-mixed; having men and women together for the root activity or location.

       co-corrections is the housing together of male and female prisoners, co-educate is to educate children of both sexes together

4. Having commonality, similarity with respect to the root.

   coaxial is having a common central axis, cobelligerent is country that wages war against a common enemy, without the countries on the same side having a formal treaty of military alliance, coaltitude is the same altitude as that of another aircraft

   2. Coequal, equal in rank.

      coadministrator is a joint administrator, coassessor is a joint assessor, cocaptain is a joint captain

   4. Indicating a family relationship that indicates a common rank made through three degrees of separation, the middle of which is by marriage.

      co-sister is one's spouse's sibling's wife, co-parent-in-law is a parent of one's child-in-law; co-husband is in a polyandrous marriage, another husband of a man’s wife

   6. Equally, equal with respect to the root.

      codominant is equally dominant, coextension is being equally extended

   8. During the same time period as the root.

      coseasonal is during a season, coseismic is during an earthquake, cotemporality is the state or characteristic of existing or occurring during the same period of time

5. (mathematics) Complementary in some formal manner.
   2. The difference from some fixed quantity.

      coaltitude is the complement of an altitude, colatitude is the difference between a latitude and 90°.

   4. Dual, relating to the opposite category.

      cocategory is the dual of a category, colimit is the dual of a limit, cocone is the dual of a cone, coalgebra is the dual of an algebra.

7. Having multiple targets or effects; the root affects or involves multiple subjects.

   coaccused is one of two or more people accused of the same offence, coaccumulation is the accumulation of two or more materials at the same time, coadsorption is the adsorption of multiple substances at the same time

9. Secondary or auxiliary in rank or priority.

   copilot is a backup or assistant pilot of an aircraft, coabuser is someone who collaborates with or refrains from interfering with an abuser in perpetrating abuse, cofeature is an auxiliary or secondary feature, coname is a secondary name

11. (biochemistry) Referring to coenzymes.

    coglucosidase is a coenzyme that activates a glucosidase, coprotease is a protease coenzyme, codehydrogenase is any dehydrogenase coenzyme

13. (organic chemistry) Referring to copolymers.

    codimer is any dimeric copolymer, copolypeptide is any polypeptide that is a copolymer, comonomer is any of a group of monomers that, when polymerized, form a copolymer

15. (chemistry) Deriving from multiple sources.

    copolymer is a polymer derived from more than one species of monomer, cointercalation is the intercalation of two or more materials, coconformation is the joint conformation of two, interacting molecules, especially that of a rotaxane

• With many terms, a hyphen (-) is used in British English, and is omitted in American English.

• (together): con-/com-/col-/cor-, syn-/syl-/sym-, inter-

• “co-”, in OneLook Dictionary Search.
• “co-”, in Merriam-Webster.com Online Dictionary, Springfield, Mass.: Merriam-Webster, 1996–present.
• John A. Simpson and Edmund S. C. Weiner, editors (1989), “co-”, in The Oxford English Dictionary, 2nd edition, Oxford: Clarendon Press, →ISBN. -- lists many derived terms

Initialism of class of.

co-

1. (informal) Initialism of class of; prefixed to a full or abbreviated year number.

   Alternative form: CO-

   Class of 2025 (co25) Graduation Information

• school class

• Oc, O. C., oc, Oc., O.C., OC

• com-, con-

From Latin co-.

co-

1. co- (together; jointly)

• “co-”, in Diccionari de la llengua catalana [Dictionary of the Catalan Language] (in Catalan), second edition, Institute of Catalan Studies [Catalan: Institut d'Estudis Catalans], April 2007
• “co-”, in Gran Diccionari de la Llengua Catalana, Grup Enciclopèdia Catalana, 2026
• “co-” in Diccionari normatiu valencià, Acadèmia Valenciana de la Llengua.

Borrowed from Latin co-.

• IPA^(key): /koː/

co-

1. co-

• Most words containing this prefix were not formed in Dutch and instead represent borrowings and internationalisms.

• IPA^(key): /ko/, /kɔ/

• Audio (France (Lyon)):

  (file)

co-

1. co- (together; jointly)

co-

1. alternative form of ko-

co-

1. co-

• (Classical Latin) IPA^(key): [kɔ]
• (modern Italianate Ecclesiastical) IPA^(key): [ko]

co-

1. allomorph of con-

Used before vowels and h, but not the consonants /j/ and /w/.

From Old Irish com-.

co-

1. co-

• Gregory Toner, Sharon Arbuthnot, Máire Ní Mhaonaigh, Marie-Luise Theuerkauf, Dagmar Wodtko, editors (2019), “com-”, in eDIL: Electronic Dictionary of the Irish Language

From co.

• IPA^(key): /t͡sɔ/

• Audio:

  (file)

• Rhymes: -ɔ
• Syllabification: co-
• Homophone: co

co-

1. forms adjectives and adverbs specifying how often something happens: -ly

   ‎co- + ‎dzienny → ‎codzienny (“daily”)

   ‎co- + ‎godzinny → ‎cogodzinny (“hourly”)

   ‎co- + ‎miesięczny → ‎comiesięczny (“monthly”)

   ‎co- + ‎roczny → ‎coroczny (“yearly”)

• “co-”, in Polish dictionaries at PWN‎^[1] (in Polish)

Learned borrowing from Latin co-.

co-

1. co-

The prefix co- only takes a hyphen when attached to words starting with h. Even so, the h may be alternatively lost. Compare coerdeiro and co-herdeiro.

• “co-”, in Dicionário Aulete Digital (in Portuguese), Rio de Janeiro: Lexikon Editora Digital, 2008–2026
• “co-”, in Dicionário Priberam da Língua Portuguesa (in Portuguese), Lisbon: Priberam, 2008–2026

• comh-

From Old Irish com-.

co-

1. Usually (but not always) designates mutuality or reciprocity.

• Gregory Toner, Sharon Arbuthnot, Máire Ní Mhaonaigh, Marie-Luise Theuerkauf, Dagmar Wodtko, editors (2019), “com-”, in eDIL: Electronic Dictionary of the Irish Language

From Latin co-.

• IPA^(key): /ko/ [ko]
• Syllabification: co-

co-

1. co-

• “co-”, in Diccionario de la lengua española [Dictionary of the Spanish Language] (in Spanish), online version 23.8.1, Royal Spanish Academy [Spanish: Real Academia Española], 15 December 2025