2. Etymology: "evening signal, ringing of a bell at a fixed hour"; from Anglo-French coeverfu, from Old French cuevrefeu; literally, "cover fire" and from Modern French couvre-few, from cuevre, covrir, "to cover" + feu, "fire".
Historical Background for curfew, "cover the fire for the night"
In the middle Ages, peasants were required to cover or to extinguish their fires at a fixed time in the evening, which was announced by the ringing of a bell called the "cover-fire" or couvre-feu in French.
Danger from fire was especially great then because most buildings were made of wood and with a strong wind, a single house which was on fire could start a conflagration or a very destructive fire that causes a great deal of damage.
The Norman French used the word in England, where it was adopted as curfu, or in modern English, curfew, referring to the hour and the signal for citizens to retire to their homes, or, as now, for the closing of a public place or the cessation of any public activity for the night.
In fact, curfew has been extended to include certain classes of people; such as, juveniles, military, etc. to withdraw from public places at a determined time; however, now it has nothing to do with "covering the fire" in homes.