Reconstruction:Proto-Celtic/sūdyā

Etymology
Oft-considered cognates include 🇨🇬, 🇨🇬, and most controversially 🇨🇬, all meaning "soot". For these three, Matasović reconstructs as their common root, independent of  from which the Germanic word was traditionally derived. The Celtic would require a metathesis of *-h₃w- to *-uh₃- in this root.

The Germanic word in particular requires what Kroonen calls "Mahlow's law", where long vowels in open syllables caused a following -w- to be lost in Germanic, for Matasović's etymology to work. Kroonen does not deal with 🇨🇬 in his dictionary.

Noun

 * 1) soot