1 a twenty-fourth part of a day and night, 60 minutes.
2 a time of day, a point in time (a late hour; what is the hour?).
3 (in pl. with preceding numerals in form 18.00, 20.30, etc.) this number of hours and minutes past midnight on the 24-hour clock (will assemble at 20.00 hours).
4 a a period set aside for some purpose (lunch hour; keep regular hours). b (in pl.) a fixed period of time for work, use of a building, etc. (office hours; opening hours).
5 a short indefinite period of time (an idle hour).
6 the present time (question of the hour).
7 a time for action etc. (the hour has come).
8 the distance traversed in one hour by a means of transport stated or implied (we are an hour from London).
9 RC Ch. a prayers to be said at one of seven fixed times of day (book of hours). b any of these times.
10 (prec. by the) each time o'clock of a whole number of hours (buses leave on the hour; on the half hour; at quarter past the hour).
11 Astron. 15° of longitude or right ascension.
Phrases and idioms:
after hours after closing-time. hour-hand the hand on a clock or watch which shows the hour. hour-long adj. lasting for one hour.
—adv. for one hour. till all hours till very late.
Etymology: ME ure etc. f. AF ure, OF ore, eure f. L hora f. Gk hora season, hour
Useful english dictionary. 2012.