Definitions for "Zeitgeber"
a periodic environmental signal that entrains a biological rhythm. For example, a cycle for a circadian rhythm, but may also be a temperature or even social cycle
Any entraining agent that plays a role in setting or resetting an internal biological clock. Examples include sunrise or sunset.
A German word literally meaning “time-giver.” A time cue capable of entraining circadian rhythms. Light represents the most important Zeitgeber.