From Proto-Italic *noktowe, from Proto-Indo-European *nokʷt-ew (“by night”). Cognate with Proto-Tocharian *nekʷtu- (“by night”) and Sanskrit अक्तु (aktú, “by night”). The noun form is either from *noctūd/*noktou, ablative and locative singular of *noktus or rebracketed from the adverb; compare Sanskrit अक्तु (aktú, “night”) and अक्तु (aktú, “by night”).