Nocturnal
late 15th century: from late Latin nocturnalis, from Latin nocturnus ‘of the night’, from nox, noct- ‘night’.
wiktionary
From Middle French nocturnal, from Latin nocturnus(“nocturnal, nightly”), from Latin nox(“night”), from Proto-Indo-European *nókʷts(“night”). Cognates include Ancient Greek νύξ(núx), Sanskrit नक्ति(nákti), Old English niht (English night) and Proto-Slavic *noťь.
etymonline
nocturnal (adj.)
"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.
