casus belli

From Latin cāsus (“case”) + bellī (“of war”). The English homographic plural casus belli is also taken from Latin, where the plural of this phrase would be cāsūs bellī, with a long vowel ū in the first word, as is typical of the nominative plural of fourth-declension nouns.

• IPA^(key): /ˈkeɪ.səs ˈbɛl.aɪ/, /- ˈbɛl.i/
• (plural) IPA^(key): /ˈkeɪ.suːs ˈbɛl.aɪ/, /- ˈbɛl.i/

casus belli (plural casus belli or casus bellis)

1. An act seen as justifying or causing a war; an act of war.
   • 1897, Congressional Record, U.S. Government Printing Office, page 664:

     The Executive, however, can do many acts which would constitute a casus belli, and thus indirectly result in war; but this does not imply in the Executive a concurrent power to declare war, and the war which would result would be one declared by a foreign power.

   • 1977, Alistair Horne, A Savage War of Peace, New York: Review Books, published 2006, page 309:

     Algiers seethed, and this was the casus belli for the ‘ultras’ to attempt a general strike.

   • 2002, Colin Jones, The Great Nation, Penguin, published 2003, page 138:

     Furthermore, if the French had airily waved away one potential casus belli, more than enough causes of potential conflict remained embedded in the Aix-la-Chapelle Treaty.

   • 2010, Christopher Hitchens, Hitch-22, Atlantic, published 2011, page 290:

     Had Saddam taken only the Rumaila oil field and the Bubiyan and Warba islands, there would have been no casus belli.

   • 2022 March 1, Mary Elise Sarotte, “I’m a Cold War Historian. We’re in a Frightening New Era.”, in The New York Times‎, →ISSN:

     And Washington needs to communicate clearly with not only its allies but also the American public on the risks involved if spillover from Ukraine into Article 5 territory verges on a casus belli — an event that provokes a war.

Borrowed from Latin.

casus belli m (invariable)

1. casus belli

Unadapted borrowing from Latin cāsus bellī.

• IPA^(key): /ˈka.zuz ˈbɛl.li/

• Audio

  (file)

• Rhymes: -ɛlli

casus belli n (indeclinable)

1. (international law) casus belli

• casus belli in Wielki słownik języka polskiego, Instytut Języka Polskiego PAN
• casus belli in Polish dictionaries at PWN

Unadapted borrowing from Latin cāsus bellī (literally “case of war”).

casus belli m (plural casuses bellis)

1. casus belli