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1530s (but not common until mid-17c.), from Latin adultus "grown up, mature, adult, ripe," past participle of adolescere "grow up, mature" (see adolescent). As a euphemism for "pornographic," it dates to 1958 and does no honor to the word.
"adult person," 1650s, from adult (adj.).
adult a·dult (ə-dŭlt', ād'ŭlt)n.
One who has attained maturity or legal age.
A fully grown, mature organism.
Euphemistically meaning unsuitable for children: adult entertainment (1950s+)