twenty-four-hour clock

or 24-hour clock

[ twen-tee-fawr-ouuhr klok, ou-er, twuhn-tee- ]

noun

1. a system of time measurement in which hours in the day are counted off consecutively from 0 to 24, with midnight being either 00:00 or 24:00. Compare twelve-hour clock ( def ).

Word History and Origins

Origin of twenty-four-hour clock¹

First recorded in 1780–90

Example Sentences

The 1300 is 1:00 p.m., written according to a twenty-four-hour clock—and PD stands for “Pirate’s Den,” an abbreviation I know well.

From Literature

The great twenty-four-hour clock at the end of the Board Room, ticking on and on while the Secretary read, wore an unfamiliar face.…Yes, time had gone wrong, somehow: and the events of the passage home to Falmouth, of the journey up to the doors of the Admiralty, though they ran on a chain, had no intervals to be measured by a clock, but followed one another like pictures on a wall.

From Project Gutenberg