An Etymological Dictionary of Astronomy and Astrophysics

The period between → sunrise and → sunset, especially the hours of darkness.

Etymology (EN): M.E., from O.E. niht (O.H.G. naht, Du., Ger. Nacht, O.N. natt, Goth. nahts), from PIE *nok(w)t- “night;” cf. Gk. nuks; L. nox (Fr. nuit; Sp. noche);
Skt. nákt-; Av. *naxtar- “night,” upa.naxtar- “adjoining the night” (Kurd. Soriani nûtak (?) “sheer darkness”); Lith. naktis; Russ. noch’.

Etymology (PE): Šab, from Mid.Pers. šab, šap “night;” O.Pers. xšap- “night;” Av. xšapan-, xšafn-, xšap- “night;” cf. Skt. ksáp- “night;” PIE base *k(w)sep- “night.”