Taint
Middle English (as a verb in the sense ‘convict, prove guilty’): partly from Old French teint ‘tinged’, based on Latin tingere ‘to dye, tinge’; partly a shortening of attaint.
wiktionary
From Middle French teint, from Old French teint (past participle of teindre(“to dye, to tinge”)), from Latin tinctum (past participle of tingere).
From Middle English taynt, aphetic form of attaynt, atteynt, from Old French atteinte(“a blow, stroke”). Compare with attaint.
Reportedly from the phrase “ 'tain't your balls and 'tain't your ass”. Ascribed to E.E. Landy's Underground Dict. (1972) is the following explanation: ‘'taint their ass and 'taint their pussy. [1]’
Contraction of it ain't.
etymonline
taint (v.)
1570s, "to corrupt, contaminate," also "to touch, tinge, imbue slightly" (1590s), from Middle English teynten "to convict, prove guilty" (late 14c.), which is partly from Old French ataint, past participle of ataindre "to touch upon, seize" (see attainder). It also is from Anglo-French teinter "to color, dye" (early 15c.), from Old French teint (12c.), past participle of teindre "to dye, color," from Latin tingere (see tincture). Related: Tainted; tainting.
taint (n.)
c. 1600, "stain, spot," from Old French teint "color, hue, dye, stain," from Latin tinctus "a dyeing," from tingere "to dye" (see tincture). Meaning "a moral stain, corruption, contaminating influence" is from 1610s.
taint
also 'taint, representing a colloquial contraction of it ain't, by 1830s, American English. The joke about the perineum involving this word dates to at least 1977.
