birthday suit birthday suit {n.} The skin with no clothes on; complete nakedness. The little boys were swimming in their birthday suits. Categories: add yours clothes {n.} Source: A Dictionary of American Idioms by A. Makkai, M.T. Boatner, J.E. Gates © 2024 To section: B Subscribe to: American IdiomsIdioms feedEnglish languageHome page and general feed Comment on this entry