An Etymological Dictionary of the German Language/Nacht
Nacht, f., ‘night,’ from the equiv. OHG. and MidHG. naht, f.; corresponding to Goth. nahts, OIc. nótt, AS. neaht, niht, E. night, Du. nacht, OSax. naht, f.; a common OTeut. naht-, f., from common Aryan nokt-, ‘night.’ Comp. Lat. nox (stem nocti-), Gr. νύξ (νυκτ-), Sans. nákta-, naktan-, n., nákti-, f., Lith. naktìs, OSlov. noštĭ. While the word ‘night’ is common to all the Aryan languages, they differ considerably in the terms for ‘day’; this is due to the fact that time in the primit. Aryan period was counted by nights and not by days; relics of this method are seen in Fastnacht, ‘Shrove Tuesday,’ Weihnachten, ‘Christmas,’ and E. fortnight, sennight (comp. Ostern and Osten). Only a few main divisions of time, such as Monat and Jahr, are widely diffused.