un·der·age I. \| ̷ ̷ ̷ ̷| ̷ ̷\adjective Etymology:under (II) + age, n. : of less than mature or legal age II. \ˈəndərij\noun (-s) Etymology:under (I) + -age : shortage, deficit III. adjective : done by or involving underage persons < underage drinking >