curfew (n.)
A curfew is an order to be off the streets after a certain hour. The word comes from the Old French cuevrefeu, cover fire.1
In medieval towns built largely of timber, a bell rang in the evening and households banked or covered their hearths for the night. A fire left untended was everybody’s problem.12
The cover itself was called a curfew too: a lid of terracotta or metal put over the embers to hold them safely until morning.2
The bell stopped and the fire went out of the meaning. By the nineteenth century the word had become what it is now, an hour after which you have to be indoors.1
The city was under curfew.