in arms . in arms {adv. phr.} Having guns and being ready to fight; armed. When our country is at war, we have many men in arms. Syn.: UP IN ARMS Categories: add yours {adv. phr.} Source: A Dictionary of American Idioms by A. Makkai, M.T. Boatner, J.E. Gates © 2024 To section: I Subscribe to: American IdiomsIdioms feedEnglish languageHome page and general feed Discuss