adult
adj.
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.
n.
"adult person," 1650s, from adult, adj..
〔李〕[ad-=to 到；ult=grown up 成长 ⇒“grown up to full size 长大成型的”→] a. fully-grown；fully developed 已成熟的；已成年的