(n.) A clock that is designed to keep very accurate time.

Big Ben alarm clock alarm watch astronomical clock atomic clock box chronometer calendar clock calendar watch chronograph chronometer chronopher chronoscope clepsydra clock clock movement clocks clockworks cuckoo clock dial digital clock digital watch electric clock electronic clock gnomon grandfather clock half-hour glass half-minute glass horologe horologium hourglass hunter independent-seconds watch isochronon journeyman marine chronometer metronome repeater sandglass sundial telltale ticker time switch timekeeper timepieces timer turnip watch watchworks wristwatch