Definition of diurnal adjective from the Oxford Advanced Learner's Dictionary

     

    diurnal

     adjective
    adjective
    BrE BrE//daɪˈɜːnl//
     
    ; NAmE NAmE//daɪˈɜːrnl//
     
     
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  1. 1(biology) (of animals) active during the day Unlike most other bats, this species is diurnal. opposite nocturnal
  2. 2(astronomy) taking one day the diurnal rotation of the earth
  3. Word Origin late Middle English (as a term in astronomy): from late Latin diurnalis, from Latin diurnus ‘daily’, from dies ‘day’.
See the Oxford Advanced American Dictionary entry: diurnal