Etymology
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caste (n.)

"one of the hereditary social groups of India," 1610s from Portuguese casta "breed, race, caste," earlier casta raça, "unmixed race," from Latin castus "cut off, separated" (also "pure," via notion of "cut off" from faults), past participle of carere "to be cut off from," from PIE *kas-to-, from root *kes- "to cut." Caste system is first recorded 1840. An earlier, now-obsolete sense of caste in English is "a race of men" (1550s), from Latin castus "chaste."

Of the castes, the first three are the natural and gradually established divisions of the Aryan invaders and conquerors of India; the fourth was made up of the subjugated aborigines. The Sanskrit name for caste is varna, color, the different castes having been at first marked by differences of complexion, according to race, and in some degree according to occupation and consequent exposure. [Century Dictionary, 1895]
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half-caste (adj.)
1789, Anglo-Indian, in reference to the offspring of a European father and an Asian mother, from half + caste.
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incest (n.)
"the crime of sexual intercourse between near kindred," c. 1200, from Old French inceste "incest; lechery, fornication," and directly from Latin incestum "unchastity, impious unchastity," also specifically "sexual intercourse between close relatives," noun use of neuter adjective incestus "unchaste, impure," from in- "not" (see in- (1)) + castus "pure" (see caste). Old English had sibleger "incest," literally "kin-lying."
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outcast (n.)

mid-14c., "an exile, a pariah, a person cast out or rejected," literally "that which is cast out," noun use of past participle of Middle English outcasten "to throw out or expel, reject," from out (adv.) + casten "to cast" (see cast (v.)). The adjective is attested from late 14c., "abject, socially despised." The verbal phrase cast out "discard, reject" is from c. 1200. In an Indian context, outcaste "one who has been expelled from his caste" is from 1876; see caste.

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chaste (adj.)

c. 1200, "virtuous, pure from unlawful sexual intercourse" (as defined by the Church), from Old French chaste "morally pure" (12c.), from Latin castus "clean, pure, morally pure" (see caste).

Transferred sense of "sexually pure" is by 15c., perhaps by influence of chastity, though chaste as a noun meaning "virgin person" is recorded from early 14c. Of language, etc., "free from obscenity," 1620s. Of artistic or literary style, "severely simple, unadorned," 1753. Related: Chastely.

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castigate (v.)

"to chastise, punish," c. 1600, from Latin castigatus, past participle of castigare "to correct, set right; purify; chastise, punish," from castus "pure" (see caste) + agere "to do" (from PIE root *ag- "to drive, draw out or forth, move"). The notion behind the word is "make someone pure by correction or reproof." Compare purge (v.), from purus + agere. Related: Castigated; castigating; castigator; castigatory.

If thou didst put this soure cold habit on To castigate thy pride, 'twere well. [Shakespeare, "Timon" IV.iii (1607)]
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chastity (n.)

c. 1200, chastete, "sexual purity" (as defined by the Church), including but not limited to virginity or celibacy, from Old French chastete "chastity, purity" (12c., Modern French chasteté), from Latin castitatem (nominative castitas) "purity, chastity" from castus "cut off, separated; pure" (see caste). Chastity-belt is from 1894 (belt of chastity is from 1878).

Chastity is merely a social law created to encourage the alliances that most promote the permanent welfare of the race, and to maintain woman in a social position which it is thought advisable she should hold. [Saturday Review, Aug. 10, 1867, quoted in Lecky, "History of European Morals," 1869]
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*kes- 
Proto-Indo-European root meaning "to cut."

It forms all or part of: caret; cashier (v.) "dismiss;" cassation; caste; castellan; castellated; Castile; castle; castigate; castrate; castration; chaste; chastity; chateau; chatelaine; Chester; forecastle; incest; quash (v.) "make void, annul."

It is the hypothetical source of/evidence for its existence is provided by: Sanskrit sastra- "knife, dagger;" Greek keazein "to split;" Latin carere "to be cut off from," cassus "empty, void;" Old Church Slavonic kosa "scythe."
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mustee (n.)

also mestee, "octoroon, offspring of a white and a quadroon," also, generally, "a half-caste," 1690s, a West Indian word, a corruption of Spanish mestizo (q.v.).

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Magus (n.)
member of the ancient Persian priestly caste, late 14c., singular of magi (q.v.).
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