incest

in-,不，非，-cest,纯的，词源同caste,castrate.即不纯洁的，引申词义乱伦。

incest

incest: [13] Etymologically, incest is virtually the same word as unchaste. It was borrowed from Latin incestus, a noun use of an adjective formed from the negative prefix in- and castus ‘pure’ (source of English chaste). The Latin word denoted ‘unchastity’ in general, but in practice was often applied specifically to ‘sexual contact between close relatives’.
=> chaste

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."

1. Her party opposes abortion, except in cases of rape or incest.

她的党派反对堕胎，但强奸或乱伦引起的怀孕除外。

2. Incest was punishable by death.

以前乱伦罪可判处死刑.

3. The " horror of incest " is not in fact universal.

“ 令人憎恶的乱伦 “ 实际上并不是普遍的.

4. Incest rules and rules of exogamy are related, not identical.

关于乱伦的规定和异族通婚的规定是有关联的, 但并不是完全相同的.

5. Mother - son incest is rare and deeply pathological.

母亲与儿子乱伦很少见也很病态.