Definition of "ultradian" []

• Relating to or exhibiting periodic physiological activity that occurs more than once every 24 hours. (adjective)

American Heritage(R) Dictionary of the English Language, Fifth Edition. Copyright (c) 2011 by Houghton Mifflin Harcourt Publishing Company. Published by Houghton Mifflin Harcourt Publishing Company. All rights reserved.

• "In fact, I, along with my twenty-four year old son, experience what is known as ultradian rapid-cycling."
• "For longer naps, test multiples of 90 minutes, which is called an "ultradian" rhythm in some papers, though the proper term should be "infradian" since it's less than 24 hours."
• "I'm ultra-rapid-cycling (ultradian) bipolar I with comorbid post-traumatic stress."