ultradian Syllabification: (ul·tra·di·an)Pronunciation: /əlˈtrādēən/Definition of ultradian 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) + -ianultradian in other Oxford dictionaries Definition of ultradian in the British & World English dictionary
