Timer
Part of speech: noun
Definition: Someone or something which times. Especially, a device used to measure the amount of time something takes, or a device that can be set to sound an alarm after a certain amount of time.
Example sentence: I wouldn't mind someone lobbing hand grenades at me, but having to reset the timer on the video recorder puts me into a blood-spitting frenzy.
Timekeeper
Part of speech: noun
Definition: A device that shows the time; a timepiece.A person who keeps records of the hours of attendance of employees.A person who records the times elapsed in a sporting event.