What is Clock?

Clock definition and meaning on Dictionary terms:
an instrument for measuring and recording time, especially by mechanical means, usually with hands or changing numbers to indicate the hour and minute: not designed to be worn or carried about.
time clock.

a meter or other device, as a speedometer or taximeter, for measuring and recording speed, distance covered, or other quantitative functioning.
biological clock.
(initial capital letter) Astronomy. the constellation Horologium.
Computers. the circuit in a digital computer that provides a common reference train of electronic pulses for all other circuits.

verb (used with object)
to time, test, or determine by means of a clock or watch: The racehorse was clocked at two minutes thirty seconds.
Slang. to strike sharply or heavily: Somebody clocked him on the face.

Verb Phrases
clock in, to begin work, especially by punching a time clock: She clocked in at 9 on the dot.
clock out, to end work, especially by punching a time clock: He clocked out early yesterday.