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ultradian ‎(comparative more ultradian, superlative most ultradian)

  1. Cyclical with a periodicity significantly shorter than 24 hours, that is, more frequent than circadian.
    • 1999, Evie Bentley, Awareness: Biorhythms, Sleep and Dreaming, page 15
      Ultradian rhythms […] operate in cycles of less than 24 hours, that is they happen more than once a day.

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