noun /ˈkəː.fjuː,ˈkɚ.fju/
a) A regulation in feudal Europe by which fires had to be covered up or put out at a certain fixed time in the evening, marked by the ringing of an evening bell.
I have my lodging neere unto a tower, where both evening and morning a very great bell doth chime Ave marie and Cover-few, which jangling doth even make the tower to shake [...].
Wikipedia foundation.