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ODE→ultradian

ultradian

Flag: gbEnglishOxford Dictionary of English
ultradian /ʌlˈtreɪdiən /
▸ adjective Physiology (of a rhythm or cycle) having a period of recurrence shorter than a day but longer than an hour. Compare with infradian
– ORIGIN 1960s: from ultra- ‘beyond’ (being of greater frequency than circadian) + -ian.