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