From Wiktionary, the free dictionary
Borrowed from Latin cāsus (“case”) + bellī (“of war”).
- IPA(key): [ˈkazʊz ˈbɛlʲɪ] (phonetic respelling: ка́зус бэ́лли)
ка́зус бе́лли • (kázus bɛ́lli) m inan (indeclinable)
- casus belli (an act seen as justifying or causing a war; act of war)