cur·few 
(kûrfy)
(kûrfy)n.
1. A regulation or rule requiring certain or all people to leave the streets or be at home at a prescribed hour.
2.
a. The time at which such a restriction begins or is in effect: a 10 PM curfew for all residents.
b. The signal, such as a bell, announcing the beginning of this restriction.
[Middle English curfeu, from Old French cuevrefeu : covrir, to cover; see COVER + feu, fire (from Latin focus, hearth).]