The Proto-Celtic word *dubu
Word *dubu
Meaning dark, black
Synonyms *luko

Other words that might be of interest
*sūl- ‘sun’, *dumāko- ‘mist’, *dengwo ‘smoke, mist’, *mūko- ‘smoke’, *dwijat ‘smoke’, *taφnos- ‘fire’, *aidu ‘fire’, *angelo- ‘fire, light’, *onno ‘ash’, *loutwi ‘ashes’, *nokʷ- ‘night’, *skalī- ‘shadow’