Proto-Celtic *dubus

→ English Doubs (derived)

→ English Doubs (derived(en/fr))

→ Breton du (inherited)

→ Welsh du (inherited)

→ Irish dubh (inherited)

→ Scottish Gaelic dubh (inherited)

→ Manx doo (inherited)

→ Cornish du (inherited)

→ Latin Dubis (derived)

→ Old Irish dub (inherited)