up in arms

up in arms (not comparable)

1. (literally) Armed for battle; prepared for or engaged in warfare.
   • c. 1592, William Shakespeare, Richard III, Act IV, Scene 4,

     March on, march on, since we are up in arms;

     If not to fight with foreign enemies,

     Yet to beat down these rebels here at home.

   • 1769, Oliver Goldsmith, The Roman History, London: S. Baker & G. Leigh, Volume 2, Chapter 18, p. 372,

     News was brought him, that the Scythians, and barbarous nations of the North, were again up in arms, and invading the empire with furious impetuosity.

2. (idiomatic) Angry; incensed; preparing for a fight.

   The union members are up in arms over threats of pay cuts.

   • 1594, Christopher Marlowe, Edward II, London: William Jones,

     Lan[caster]. My lord, will you take armes against the king?

     Bish[op]. What neede I, God himselfe is vp in armes,

     When violence is offered to the church.

   • 1728, Henry Fielding, The History of Tom Jones, a Foundling, Dublin: John Smith, Volume 3, Book 18, Chapter 5, p. 301,

     Allworthy was of a cooler Disposition than the good Woman, whose Spirits were all up in Arms in the Cause of her Friend.

   • 2003, David Diamond, “The Way We Live Now: 9-28-03: Questions for Linus Torvalds; The Sharer,” The New York Times Magazine, 28 September, 2003,

     Is file-sharing, which has the recording industry so up in arms, the “dark side” of open-source attitudes?

• The expression is rarely used in its literal sense in contemporary English.
• "All" may be added as an intensifier at the beginning of the expression, as in:

Her father was all up in arms when we returned late at night.