From Longman Dictionary of Contemporary Englishone o'clock/two o'clock etcone o'clock/two o'clock etcTMCone of the times when the clock shows the exact hour as a number from 1 to 12 It’s already 9 o'clock. The meeting is at 10 o'clock. ► Do not use o'clock when mentioning minutes or parts of an hour: ten past nine (NOT ten past nine o'clock) | half past one (NOT half past one o'clock). Do not use o'clock when writing the time in the form 1.00,2.00 etc. → o'clock
