cheat on

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cheat on (third-person singular simple present cheats on, present participle cheating on, simple past and past participle cheated on)

1. Used other than figuratively or idiomatically: see cheat,‎ on.

   I was disqualified for cheating on my final exam.

2. (colloquial, idiomatic, transitive) To be unfaithful to, especially in a romantic relationship.

   Six years of a happy relationship, and then she had the nerve to cheat on me with a barman!

• have an affair