"of or pertaining to the night, used or done at night," late 15c. (Caxton), 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. Related: Nocturnally. Nocturnal emission "involuntary ejaculation during sleep" is recorded by 1813.
updated on July 01, 2019