Definition of incest noun from the Oxford Advanced Learner's Dictionary

 

incest

 noun
noun
BrE BrE//ˈɪnsest//
 
; NAmE NAmE//ˈɪnsest//
 
[uncountable]
 
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sexual activity between two people who are very closely related in a family, for example, a brother and sister, or a father and daughter incest between brother and sister taboos forbidding incest Word Origin Middle English: from Latin incestus, incestum ‘unchastity, incest’, from in- ‘not’ + castus ‘chaste’.
See the Oxford Advanced American Dictionary entry: incest