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1. Sexual relations between persons closely related by blood, especially between parents and children, brother and sister. 2. The crime of sexual relations between persons related by blood, where such cohabitation is prohibited by law. [L. incestus, unchaste, fr. in-, not, + castus, chaste]
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in·cest 'in-.sest n sexual intercourse between persons so closely related that they are forbidden by law to marry also the statutory crime of engaging in such sexual intercourse
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in·cest (inґsest) [L. incestus impure] sexual intercourse or other sexual activity between persons so closely related that marriage between them is legally or culturally prohibited.Medical dictionary. 2011.