The hour after midnight, when witches and other supernatural beings were thought to be active, and to which bad luck was ascribed.

The regular times of day when a shop, office or similar is open to the public.

(time) fifteen minutes.

The scheduled time for the start of some event, especially a military operation; H-hour.

The times, typically from about 9am to 5pm, Monday to Friday, when non-24/7 office workers are at their desks.

(electricity) A unit of energy equal to that done by one kilowatt acting for one hour.

(idiomatic) A point in time which is nearly too late; the last minute.

The number of credit hours a student takes in a semester, usually for a college or university to count towards a degree.

plural of canonical hour.

A time of day, usually in the afternoon or early evening, when a bar or pub offers its drinks at a discounted price.