The definition of diurnal is something that happens daily or in the daytime.(adjective)
An example of something diurnal is a diurnal flower that blooms in the sunlight, but closes at night.
See diurnal in Webster's New World College Dictionary
Origin: ME < L diurnalis < diurnus, daily < dies, day: see deity
See diurnal in American Heritage Dictionary 4
Origin: Middle English
Origin: , from Late Latin diurnālis
Origin: , from Latin diurnus
Origin: , from diēs, day; see dyeu- in Indo-European roots.
Learn more about diurnal