casus belli: meaning, definition, pronunciation and examples
C2Formal, Academic, Diplomatic
Quick answer
What does “casus belli” mean?
An act or event that justifies or is used as the formal pretext for initiating a war.
Audio
Pronunciation
Definition
Meaning and Definition
An act or event that justifies or is used as the formal pretext for initiating a war.
A cause or reason for a serious dispute, conflict, or drastic action, often with formal or deliberate overtones.
Dialectal Variation
British vs American Usage
Differences
No significant difference in meaning or usage. Slightly more common in British formal/academic writing due to historical and diplomatic tradition.
Connotations
Connotes calculated, often cynical, political or diplomatic justification rather than a spontaneous emotional reason for conflict.
Frequency
Very low frequency in both varieties, almost exclusively found in scholarly, historical, or political discourse.
Grammar
How to Use “casus belli” in a Sentence
The (attack/incident) served as a casus belli.They sought a casus belli for (war/intervention).The government used (X) as a casus belli.Vocabulary
Collocations
Usage
Meaning in Context
Business
Metaphorically, a hostile takeover bid could be described as providing a 'casus belli' for a corporate war.
Academic
A standard term in historical and political science texts discussing the origins of conflicts, e.g., 'The assassination provided the casus belli for World War I.'
Everyday
Extremely rare; might be used hyperbolically in formal conversation to describe a serious personal provocation.
Technical
A precise term in international law and diplomatic studies referring to an act justifying war under international norms.
Vocabulary
Synonyms of “casus belli”
Strong
Neutral
Weak
Vocabulary
Antonyms of “casus belli”
Watch out
Common Mistakes When Using “casus belli”
- Incorrect plural: 'casus bellis' (correct: 'casus belli', used as an invariant plural or 'causes belli').
- Incorrect pronunciation: confusing 'belli' with 'bell-ee' instead of 'bel-lye' or 'bel-lee'.
- Using it for minor disputes, which diminishes its gravity.
FAQ
Frequently Asked Questions
Yes, it is a loan phrase from Latin, fully naturalised into English, particularly in formal, historical, and political discourse. It is found in major English dictionaries.
The phrase is often used as invariable ('several casus belli'). The technically correct Latin plural is 'casus belli' (same form) or the Anglicised 'causes belli'. 'Casus bellis' is incorrect.
Yes, but it is a deliberate metaphorical extension. Using it for a business dispute or major personal conflict is stylistically marked and implies a formal, serious, and strategically chosen provocation.
A 'casus belli' is the stated or formal justification for war. A 'pretext' implies the reason is false or invented. In practice, a 'casus belli' can be a genuine grievance or a mere pretext, depending on the historical perspective.
An act or event that justifies or is used as the formal pretext for initiating a war.
Casus belli is usually formal, academic, diplomatic in register.
Casus belli: in British English it is pronounced /ˌkɑːsʊs ˈbɛliː/, and in American English it is pronounced /ˌkeɪsəs ˈbɛlaɪ/. Tap the audio buttons above to hear it.
Learning
Memory Aids
Mnemonic
Think of 'CASE' (casus) of 'BELLIgerence'. A specific case that causes belligerent (war-like) action.
Conceptual Metaphor
WAR/ CONFLICT IS A FORMAL LEGAL CASE (The reason for war is treated as a case to be presented and argued).
Practice
Quiz
In which context would the use of 'casus belli' be MOST appropriate?