of or relating to a biorhythm having a period of less than 24 hours.
Origin of ultradian
Dictionary.com Unabridged Based on the Random House Unabridged Dictionary, © Random House, Inc. 2019
Relating to or exhibiting periodic physiological activity that occurs more than once every 24 hours.
The American Heritage® Stedman's Medical Dictionary Copyright © 2002, 2001, 1995 by Houghton Mifflin Company. Published by Houghton Mifflin Company.