Comparative evidence

negʷ

• Hitt. neku- 'become evening' (CHD L-N: 432, EDHIL: 602)

• Hitt. nekuz 'evening', 'nightfall', 'dawn', 'twilight' (CHD L-N: 434ff.)

• Hitt. nana(n)kuss- 'be dark', 'become dark', 'become obscure' (EDHIL: 595f.)

References

EDHIL = Kloekhorst, A. 2008. Etymological Dictionary of the Hittite Inherited Lexicon. Brill.
CHD = Guterbock H.G., H.A. Hoffner, Th.P.J. van den Hout (eds.), 1980 - . The Hittite Dictionary of the Oriental Institute of the University of Chicago. Chicago.