Merriam-Webster Collegiate Dictionary - curfew

 noun  Etymology: Middle English, from Anglo-French coverfeu, signal given to bank the hearth fire, ~, from coverir to cover + fu, feu fire, from Latin focus hearth  Date: 14th century  1. the sounding of a bell at evening the Curfew tolls the knell of parting day — Thomas Gray  2.  a. a regulation enjoining the withdrawal of usually specified persons (as juveniles or military personnel) from the streets or the closing of business establishments or places of assembly at a stated hour  b. a signal to announce the beginning of a ~  c. the hour at which a ~ becomes effective  d. the period during which a ~ is in effect