Hour  n. 1 twenty-fourth part of a day and night, 60 minutes. 2 time of day, 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 period for a specific purpose (lunch hour; keep regular hours). B (in pl.) Fixed working or open period (office hours; opening hours). 5 short period of time (an idle hour).