twelve-hour clock

or 12-hour clock

[ twelv-ouuhr klok, ou-er ]

noun

1. a system of time measurement in which the day is divided into two twelve-hour periods, both midnight and noon are 12:00, and the hours following each are numbered from 1:00 to 11:00 a.m. or p.m. Compare twenty-four-hour clock ( def ).

Word History and Origins

Origin of twelve-hour clock¹

First recorded in 1870–80