Phrase guide

casus belli

noun · 2 senses · updated from the 2026-07-25 local source snapshot

Definitions and examples are grouped by meaning. Pronunciation, history, word forms, translations, descendants, synonyms, antonyms, derived terms, and related words appear whenever the source provides them.

Sound

Pronunciation

Each Play button uses your device's default local English voice, or a natural local fallback. The selected voice name appears after playback. This is synthesized speech, not a source recording.

  • /ˈkeɪ.səs ˈbɛl.aɪ/
  • /ˌkɑː-/
  • /-ˈbɛl.i/
  • Southern-England: Recorded audio is listed in the source snapshot.

1

noun

Meaning 1

An act seen as justifying or causing a war; an act of war.

Definition source: English Wiktionary via Wiktextract

Examples

  • In ancient times, repeatedly failing to pay tribute by a vassal state was often used as a casus belli by the patron.

Meaning relationships

Synonyms: none provided

Antonyms: none provided

2

noun

Meaning 2

an event used to justify starting a war

Definition source: Princeton WordNet 3.0

No example sentence was provided for this meaning.

Meaning relationships

Synonyms: none provided

Antonyms: none provided

Broader terms: beginning

History

Etymology

From Latin cāsus (“occasion”) + bellī (“for war”, literally “of war”).

Across languages

Translations

31 source translations are retained for this English entry.

  • Arabic: ذَرِيعَةُ الْحَرْبِ (ḏarīʕatu al-ḥarbi) — act causing war
  • Armenian: կազուս բելլի (kazus belli) — act causing war
  • Belarusian: ка́зус бэ́лі (kázus béli) — act causing war
  • Catalan: casus belli — act causing war
  • Chinese Mandarin: 戰爭藉口 /战争借口 (zhànzhēng jièkǒu) — act causing war
  • Chinese Mandarin: 開戰理由 /开战理由 (kāizhàn lǐyóu) — act causing war
  • Finnish: sodan aihe — act causing war
  • Finnish: casus belli — act causing war
  • French: casus belli — act causing war
  • Georgian: კაზუს ბელი (ḳazus beli) — act causing war
  • German: Casus Belli — act causing war
  • German: Kriegsgrund — act causing war
  • Bavarian German: Kasus Belli — act causing war
  • Greek: αφορμή πολέμου (aformí polémou) — act causing war
  • Indonesian: casus belli — act causing war
  • Italian: casus belli — act causing war
  • Japanese: 開戦理由 (kaisen riyū) — act causing war
  • Japanese: 開戦事由 (kaisen jiyū) — act causing war
  • Korean: 개전 이유 (gaejeon iyu) — act causing war
  • Korean: 개전 리유 (gaejeon riyu) — act causing war
  • Korean: 전쟁 명분 (jeonjaeng myeongbun) — act causing war
  • Latin: cāsus bellī — act causing war
  • Persian: بهانهٔ جنگ (bahâne-ye jang) — act causing war
  • Persian: کیسوس بللی (keysus belli) — act causing war
  • Polish: casus belli — act causing war
  • Portuguese: casus belli — act causing war
  • Russian: ка́зус бе́лли (kázus bɛ́lli) — act causing war
  • Thai: เหตุแห่งสงคราม (hèet-hɛ̀ɛng-sǒng-kraam) — act causing war
  • Turkish: harp sebebi — act causing war
  • Turkish: savaş nedeni — act causing war
  • Ukrainian: ка́зус бе́ллі (kázus bélli) — act causing war