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incest

[in-sest]
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noun
  1. sexual intercourse between closely related persons.
  2. the crime of sexual intercourse, cohabitation, or marriage between persons within the degrees of consanguinity or affinity wherein marriage is legally forbidden.
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Origin of incest

1175–1225; Middle English < Latin incestus (noun) sexual impurity, derivative of incestus (adj.) profane, sexually impure (in- in-3 + -cestus combining form of castus chaste), by analogy with v. nouns derived with -tus
Dictionary.com Unabridged Based on the Random House Unabridged Dictionary, © Random House, Inc. 2018

British Dictionary definitions for incests

incest

noun
  1. sexual intercourse between two persons commonly regarded as too closely related to marry
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Word Origin

C13: from Latin incestus incest (from adj: impure, defiled), from in- 1 + castus chaste
Collins English Dictionary - Complete & Unabridged 2012 Digital Edition © William Collins Sons & Co. Ltd. 1979, 1986 © HarperCollins Publishers 1998, 2000, 2003, 2005, 2006, 2007, 2009, 2012

Word Origin and History for incests

incest

n.

c.1200, "the crime of sexual intercourse between near kindred," from Old French inceste and directly from Latin incestum "unchastity, impious unchastity," also specifically "sex between close relatives," noun use of neuter adjective incestus "unchaste, impure," from in- "not" (see in- (1)) + castus "pure" (see caste). In early use also in reference to sexual relations or marriage with one under a vow of chastity (sometimes distinguished as spiritual incest). Old English had sibleger "incest," literally "kin-lying."

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Online Etymology Dictionary, © 2010 Douglas Harper

incests in Medicine

incest

(ĭnsĕst′)
n.
  1. Sexual relations between persons who are so closely related that their marriage is illegal or forbidden by custom.
  2. The statutory crime of sexual relations with such a near relative.
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The American Heritage® Stedman's Medical Dictionary Copyright © 2002, 2001, 1995 by Houghton Mifflin Company. Published by Houghton Mifflin Company.

incests in Culture

incest

Sexual relations between relatives who are forbidden by law to marry; for example, between father and daughter or mother and son.

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Note

Though each society has its own system for determining the range of people who fall into this category, every society has an incest taboo of some sort.
The New Dictionary of Cultural Literacy, Third Edition Copyright © 2005 by Houghton Mifflin Harcourt Publishing Company. Published by Houghton Mifflin Harcourt Publishing Company. All rights reserved.