WordReference Random House Unabridged Dictionary of American English © 2025
at•ta•boy
(at′ə boi′),USA pronunciation interj. [Informal.]
- (used as an enthusiastic expression of encouragement or approval to a boy, man, or male animal.)
- alleged to be a reduced form of that's a boy or that's the boy 1905–10, American.
'attaboy' also found in these entries (note: many are not synonyms or translations):