timepiece, timekeeper

a measuring instrument or device for keeping time

• atomic clock — a timepiece that derives its time scale from the vibration of atoms or molecules
• clock — a timepiece that shows the time of day
• sandglass — timepiece in which the passage of time is indicated by the flow of sand from one transparent container to another through a narrow passage
• sundial — timepiece that indicates the daylight hours by the shadow that the gnomon casts on a calibrated dial
• timer — a timepiece that measures a time interval and signals its end
• watch, ticker — a small portable timepiece

• measuring instrument, measuring system, measuring device — instrument that shows the extent or amount or quantity or degree of something

• balance wheel — a wheel oscillating against the hairspring of a timepiece to regulate its beat
• dial — the face of a timepiece; graduated to show the hours
• escapement — mechanical device that regulates movement
• hairspring — a fine spiral spring that regulates the movement of the balance wheel in a timepiece
• hand — a rotating pointer on the face of a timepiece
• time-ball — a ball that slides down a staff to show a fixed time; especially at an observatory