1. A man or woman who is fully grown up; a mature person. In his humorous dictionary published as The Penthouse Sexicon (1968), Frederic Mullally defines:
-- Adult: ' Person who is supposed to know what he or she is doing.'
-- Adulterer: ' Person who does it.'
-- Adultery: ' It.'
2. One who has reached the age of majority or legal age, now generally 18 years. Synonyms: grown; grown-up; mature(d); of age. Antonym: underage(d).