1. of or relating to the night (opposed to diurnal).
  2. done, occurring, or coming at night: nocturnal visit.
  3. active at night (opposed to diurnal): nocturnal animals.
  4. opening by night and closing by day, as certain flowers (opposed to diurnal).
  1. Archaic. an astrolabe for telling time at night or for determining latitude by the position of certain stars in reference to Polaris.

Origin of nocturnal

From the Late Latin word nocturnālis, dating back to 1475–85. See nocturn, -al1
Related formsnoc·tur·nal·i·ty, nounnoc·tur·nal·ly, adverbnon·noc·tur·nal, adjectivenon·noc·tur·nal·ly, adverbsem·i·noc·tur·nal, adjectiveun·noc·tur·nal, adjectiveun·noc·tur·nal·ly, adverb
Can be confuseddiurnal nocturnal

Synonyms for nocturnal Unabridged Based on the Random House Unabridged Dictionary, © Random House, Inc. 2018

British Dictionary definitions for nocturnality


  1. of, used during, occurring in, or relating to the night
  2. (of animals) active at night
  3. (of plants) having flowers that open at night and close by day
Compare diurnal
Derived Formsnocturnality, nounnocturnally, adverb

Word Origin for nocturnal

C15: from Late Latin nocturnālis, from Latin nox night
Collins English Dictionary - Complete & Unabridged 2012 Digital Edition © William Collins Sons & Co. Ltd. 1979, 1986 © HarperCollins Publishers 1998, 2000, 2003, 2005, 2006, 2007, 2009, 2012

Word Origin and History for nocturnality



late 15c., from Old French nocturnal "nightly, nocturnal," or directly from Late Latin nocturnalis, from Latin nocturnus "belonging to the night," from nox (genitive noctis) "night," cognate with Old English neaht (see night) + -urnus, suffix forming adjectives of time. Nocturnal emission "involuntary ejaculation during sleep" first recorded 1813.

Online Etymology Dictionary, © 2010 Douglas Harper

nocturnality in Medicine


  1. Of, relating to, or occurring in the night.
  2. Most active at night.
The American Heritage® Stedman's Medical Dictionary Copyright © 2002, 2001, 1995 by Houghton Mifflin Company. Published by Houghton Mifflin Company.

nocturnality in Science


  1. Occurring at night.
  2. Most active at night. Many animals, such as owls and bats, are nocturnal.
  3. Having flowers that open during the night and close at daylight. Nocturnal plants are often pollinated by moths. Compare diurnal.
The American Heritage® Science Dictionary Copyright © 2011. Published by Houghton Mifflin Harcourt Publishing Company. All rights reserved.