DICT.TW Dictionary Taiwan

 ca·sus bel·li /ˈkɑsəsˈbɛˌli, ˈkesəsˈbɛˌlaɪ/
 開戰理由

 Ca·sus n.  An event; an occurrence; an occasion; a combination of circumstances; a case; an act of God. See the Note under Accident.
 Casus belli, an event or combination of events which is a cause war, or may be alleged as a justification of war.
 Casus fortuitus, an accident against which due prudence could not have provided. See Act of God, under Act.
 Casus omissus, a case not provided for by the statute.
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 casus belli
      n : an event used to justify starting a war