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Adjective: diurnal  dI'ur-n(u)l
  1. (biology) 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. Having a daily cycle or occurring every day
    "diurnal rotation of the heavens"

See also: periodic, periodical

Antonym: nocturnal

Encyclopedia: Diurnal