/ əˈdʌltəri; NAmE / noun
[ U ] sex between a married person and sb who is not their husband or wife :
He was accused of committing adultery .
► adul·ter·ous / əˈdʌltərəs; NAmE / adjective :
an adulterous relationship
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WORD ORIGIN
late 15th cent.: from the obsolete noun adulter , from Latin adulter adulterer, replacing an earlier form avoutrie , from Old French avouterie .