S: (n) atomic clock (a timepiece that derives its time scale from the vibration of atoms or molecules)
S: (n) clock (a timepiece that shows the time of day)
S: (n) 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)
S: (n) sundial (timepiece that indicates the daylight hours by the shadow that the gnomon casts on a calibrated dial)
S: (n) timer (a timepiece that measures a time interval and signals its end)