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ultradian (adj) – Relating to or exhibiting periodic physiological activity that occurs more than once every 24 hours.

Source : The Free Dictionary

Etymology : The English adjectives ultradian and circadian are close contemporaries?1961 for ultradian, 1959 for circadian. Both adjectives refer to biological or physiological cycles, ultradian meaning ?recurring with a period shorter than a day,? and circadian ?recurring with a period of approximately 24 hours.? Both adjectives have similar formations: the Latin prefix ultra- meaning ?beyond, on the far side of? and circa meaning ?around, about.? The element -dian is formed from the Latin noun di?s ?day? and the English adjective suffix -an, from Latin -?nus.