Is there an abbreviation of “can not”? [closed]

Not abbreviation. It's called contraction.

Contraction: A contraction is a word made by shortening and combining two words.

Examples:

Cannot -> can't

Do not -> don't

Does not -> doesn't

Will not -> won't

Would not -> wouldn't etc.

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Writing contractions: All contractions include a punctuation mark called apostrophe (').

The apostrophe replaces any letters that are present in the original words but absent in the contraction.

The contraction, for example, wouldn't means would not. As you can see, the O in not is not present in couldn't. The apostrophe goes in its place, right between the n and t.

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Cannot -> can't

It's pronunciation is different in AmE and BrE.

BrE: /kɑːnt/ (like kaant)

AmE: /kænt/ (same as can but add t)

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Here's a long explanation about contractions: https://dictionary.cambridge.org/grammar/british-grammar/contractions

NOTE: Avoid contractions in formal writing, such as business letters, essays, technical papers, research papers and exams.

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