sack in/out . sack in/out {v.}, {slang} To go to sleep for a prolonged period (as in from night to morning). Where are you guys going to sack in/sack out? Categories: add yours {slang} {v.} Source: A Dictionary of American Idioms by A. Makkai, M.T. Boatner, J.E. Gates © 2024 To section: S Subscribe to: American IdiomsIdioms feedEnglish languageHome page and general feed Discuss