Circannual

Origin

Formed as circa + annual, after circadian.

Full definition of circannual

Adjective

1. (biology) Occurring or having cycles of approximately annual periodicity
• 1956, USAF School of Aerospace Medicine, Report 80-114, 1956, page 11… because morbidity and mortality from cardiovascular disease also reveal statistically significant circadian and circannual rhythms.
• 2000, Martin Hume Johnson, Barry J. Everitt, Essential Reproduction, page 110Circannual rhythms control reproductive function in seasonal breeders.
• 2001, Joseph S. Takahashi, Fred W. Turek, Robert Y. Moore, Handbook of Behavioral Neurobiology, page 523Seasonal variations in locomotor activity are generated by a circannual clock ….

Usage notes

In practice circannual is not used comparatively. In principle, one biorhythm could be "more circannual" than another if its period were closer to a year than the other's.