zeitgeber n. Light and temperature are the only periodic or quasi-periodic environmental variables to which endogenous oscillation can be coupled: in nature they entrain the endogenous oscillation, thereby controlling period and establishing appropriate phase. They are, to use Aschoff’s phrase, the principal Zeitgeber. [GermanUnited StatesScienceJargon] [full cite] (Jun. 5, 2004)
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. [GermanScienceJargon] [full cite] (Jun. 5, 2004)