zeitgeber

[tsahyt-gey-ber]
noun
  1. an environmental cue, as the length of daylight or the degree of temperature, that helps to regulate the cycles of an organism's biological clock.

Origin of zeitgeber

1970–75; < German (1954), literally, time-giver, on the model of Taktgeber an electronic synchronization device
Dictionary.com Unabridged Based on the Random House Unabridged Dictionary, © Random House, Inc. 2018