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diurnal - of or belonging to or active during the day; diurnal animals are active during the day; diurnal flowers are open during the day and closed at night; diurnal and nocturnal offices. 2. diurnal - having a daily cycle or occurring every day; diurnal rotation of the heavens.
Princeton's WordNet (0.00 / 0 votes) Rate this definition: nocturnal (adj). belonging to or active during the night. nocturnal animals are active at night; nocturnal plants have flowers that open at night and close by day. nocturnal (adj). of or relating to or occurring in the night. nocturnal darkness.