Casus \Ca"sus\, n. [L.]

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.

Source: Webster's Revised Unabridged Dictionary (1913)