up in arms

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up in arms (not comparable)

1. Armed for battle; prepared for or engaged in warfare.
   • c. 1593 (date written), William Shakespeare, “The Tragedy of Richard the Third: […]”, in Mr. William Shakespeares Comedies, Histories, & Tragedies […] (First Folio), London: […] Isaac Iaggard, and Ed[ward] Blount, published 1623, OCLC 606515358, [Act IV, scene iv]:

     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. (figuratively) Angry; incensed; preparing for a fight.

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

   • 1594 (first publication), Christopher Marlow[e], The Trovblesome Raigne and Lamentable Death of Edvvard the Second, King of England: […], London: […] [Eliot’s Court Press] for Henry Bell, […], published 1622, OCLC 837836359, (please specify the page):

     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.

   • 1749, Henry Fielding, chapter 5, in The History of Tom Jones, a Foundling, volume (please specify |volume=I to VI), London: A[ndrew] Millar, […], OCLC 928184292, book 18, page 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.

• in arms
• under arms

• “be up in arms” in Longman Dictionary of Contemporary English, Longman.
• “be up in arms” in the Cambridge English Dictionary, Cambridge: Cambridge University Press.
• “up in arms” in the Cambridge English Dictionary, Cambridge: Cambridge University Press.
• “up in arms” (US) / “up in arms” (UK) in Macmillan English Dictionary.