Casus

n.
  1. An event; an occurrence; an occasion; a combination of circumstances; a case; an act of God. See the Note under Accident.
    2. 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.