"Co" implies partnership and togetherness in many technical contexts, e.g., co-planar (located in the same plane), co-orbital (moving in the same orbit), etc.

Which prefix is the antonym of "co" whose usage reverses the meaning of the words like co-planar?

  • 3
    Like "non-co-planer" and "non-co-orbital"? – Davo Aug 6 '19 at 14:32
  • @Davo: As a person who's not a native speaker, I thought adding back-to-back prefixes would sound awkward to native speakers' ears. But if you suggest them, they wouldn't have such impact ;-) – Pinton Aug 6 '19 at 14:53
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    I don't believe that there is a specific prefix; @Davo's usage is what I hear - and use - all the time. – Jeff Zeitlin Aug 6 '19 at 15:01
  • I don't really understand the question. Take co-president. If you're talking about a single president, you simply remove the prefix altogether: president. The lack of the prefix already implies a singular thing. Or do you mean to "reverse" it in some other way? – Jason Bassford Aug 6 '19 at 15:13
  • The reverse condition in the planar example is nonplanar but there is no rule, and there are various prefixes in use which mean "not". – Weather Vane Aug 6 '19 at 15:46

As suggested in the comments (thanks @Weather Vane, @Davo, @Jeff Zeitlin), there is no general rule for an antonym to "co-". It depends on the context.

In some cases, you can add more than one prefix to the word, but be aware that this can make the wording sound very technical, formal or stiff:

Co-planar can become non-coplanar

Cooperate can become non-cooperative or simply not cooperative

Many "co-" words do not have a simple antonym at all:

Coeducational becomes divided, separate or segregated.

Cohabit (from cohabitation) becomes disjoin, or simply break up or move out


There is no simple prefix like "anti" that universally does what you need.

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