a person or thing that keeps time.

an official appointed to time, regulate, and record the duration of a sports contest or its component parts, as to give the official time of a race, assure that a round of boxing is ended exactly on time, or announce to football, basketball, hockey, etc., teams the amount of time left to play.

a timepiece

This watch is a good timekeeper.

a person employed to keep account of the hours of work done by others.

a person who beats time in music.