zeitgeber
 n.— «All three of us redefined our terms, they a zeitgeber and I a synchronizer (as primary or secondary), respectively, as an external agent, usually a cycle that does not “give” time and merely synchronizes existing body time with its own.» —“Transdisciplinary unifying implications of circadian findings in the 1950s” by Franz Halberg Journal of Circadian Rhythms Sept. 24, 2003. (source: Double-Tongued Dictionary)