|1.||[ adjective ] (biology) 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"
|Related terms:||nocturnal biology daytime|
|2.||[ adjective ] having a daily cycle or occurring every day|
"diurnal rhythms" "diurnal rotation of the heavens" "the diurnal slumber of bats"