of physiological cycles longer than an hour and shorter than a day
Relating to biologic variations or rhythms occurring in cycles more frequent than every 24 hours. ... Compare: circadian, infradian. ... Origin: ultra-+ L. Dies, day ... (05 Mar 2000) ... 
(ul″trә-de´әn) pertaining to a period of less than 24 hours; applied to the rhythmic repetition of certain phenomena in living organisms occurring in cycles of less than a day. See also ultradian rhythm.
Type: Term Pronunciation: ŭl-trā′dē-ăn Definitions: 1. Relating to biologic variations or rhythms occurring in cycles more frequent than every 24 hours.
of or pertaining to a biorhythm having a period of less than 24 hours.