The Proto-Indo-European word *nebʰ-o-, nebʰ-i-
Word *nebʰ-o-, nebʰ-i-
Meaning cloud
See also Hittite: ne-e-pi-iš ‘sky, heaven’
Synonyms *sneudh-, *nébʰes-

Comments
Lat. nebŭlō, OCS nebo, Russ. nebo, Skr. nabhas, Gk. nephos, Hitt. nepiš, Lyc. tabahaza, Luw. tappaš-, Gm. nebul/Nebel, Eng. nifol/--, Welsh nef, Kamviri niru, Polish niebo, Lith. debesis, Ltv. debess, Av. nabah, Ir. nem/neamh, ON niflhel

Other words that might be of interest
*ĝheim- ‘snow, winter’, *h₂stḗr ‘star’, *méh₁-nōt ‘moon, month’, *sneigʷh- ‘snow’, *séhₐul ‘sun’, *h₃meigh- ‘drizzle, mist’, *(s)kand- ‘shine, glitter, moon’, *louksnehₐ- ‘moon’