What does "casus belli" mean?

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

What is a synonym for "casus belli"?

Common synonyms include: affront, bone of contention, offense, rub, slap in the face, sore spot.

Pronounced //ˈkeɪ.səs ˈbɛl.aɪ//.

/ˈkeɪ.səs ˈbɛl.aɪ/ noun

noun ·Rare ·Advanced level

Noun

1
An act seen as justifying or causing a war; an act of war.
"In ancient times, repeatedly failing to pay tribute by a vassal state was often used as a casus belli by the patron."
2
an event used to justify starting a war wordnet

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

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