SpeakUP Academy

Resources

Lecciones de gramáticaPor temasFlash cardsLecturasEjercicios de listeningGlosarioFalsos amigos¿Cuál usar?SufijosPrefijos
Discover your levelBlog
ESEN

Prefix · joint action / together

co-/com-/con-

Signals joint action or union: cooperate, combine, connect, coexist, coworker.

Basic

Written by Bryan López, English teacher · Updated

What does the prefix co- mean?

Co- comes from the Latin cum, which means "with" or "together". It shows joint action: people or things doing something as a team. The central idea is always "more than one, working together". Besides co-, it has two more forms (com- and con-), which we explain on the con- page.

Co- is the prefix that creates new words

Of its three forms, co- is the most productive today: you can attach it to a job or role to say you do it with someone else. When the word is new or uncommon, it is sometimes written with a hyphen. If you are not sure whether to use a hyphen, check the dictionary. Because it is so flexible, co- is the one you are most likely to meet in brand-new words.

How it is used

The variant depends on the first letter of the root:

  • co- + vowel or modern root
    operate → cooperateexist → coexistauthor → coauthorworker → coworker
  • com- + p, b, m
    bine → combinepress → compresspete → competeplete → complete
  • con- + consonant
    nect → connectfirm → confirmtrol → controlduct → conduct

Co- is the most visible and productive variant in modern English: co-founder, co-host, co-pilot. Com- and con- appear almost exclusively in already-established words.

How it is pronounced

co-/com-/con-/koʊ/, /kɒm/, /kɒn/

Tap the button to hear how the prefix sounds. Each word in the table has its own audio.

Examples

  • operatecooperateThe two departments agreed to cooperate on the project.
  • existcoexistDifferent cultures can coexist peacefully with mutual respect.
  • workercoworkerShe thanked every coworker who helped with the launch.
  • binecombineThe chef likes to combine unexpected flavours in his dishes.
  • nectconnectThe new bridge will connect both sides of the city.
  • authorcoauthorThey decided to coauthor the report for equal credit.
  • foundercofounderShe is listed as a cofounder despite joining months later.

Common mistakes

co- always needs a hyphen (co-worker, co-exist)
the hyphen is optional and increasingly dropped in modern English

"Coworker" and "co-worker" are both correct. American English tends to drop the hyphen; British English keeps it more often.

cooperate = simply doing the same thing as someone else
cooperate = actively working together toward a shared goal

"Cooperate" implies active, deliberate collaboration. It is also used in formal and legal contexts: "the suspect cooperated with police."

A trick to remember it

Picture two people working shoulder to shoulder: co- = together with. cooperate, combine.

Practise what you learned

Exercise 1 · Form the word

The two scientists decided to ___ on the paper and share credit for the findings equally.

Hint: co- + author = ?

Exercise 2 · Pick the right one

"The two rival companies decided to ___ on the research project to share costs and expertise."

Exercise 3 · Pick the right one

Which word does NOT use co-/com-/con- with the sense of "together or union"?

Frequently asked questions

What does the prefix co-/com-/con- mean in English?

The prefix co-/com-/con- signals joint action or union: cooperate, combine, connect, coexist, coworker.

How do you pronounce co-/com-/con-?

The prefix co-/com-/con- is pronounced /koʊ/, /kɒm/, /kɒn/. For example, "cooperate".

Can you give an example of a word with co-/com-/con-?

"operate" becomes "cooperate". It is a typical example of the co-/com-/con- prefix.

Other useful prefixes

Learn every English prefix

un-, re-, pre-, dis-, over-, in-... every beginning you need to unlock thousands of English words at once.

View all prefixes