Longman Dictionary English

From Longman Dictionary of Contemporary Englishincestin‧cest /ˈɪnsest/ noun [uncountable] SYSEX/HAVE SEX WITHsex between people who are closely related in a family Abortions would only be allowed in cases of rape or incest.Origin incest (1200-1300) Latin incestum, from castus “pure”; → CHASTE
ldoceonline.com