Welsh dwfn

← Proto-Brythonic *duβn (inherited)

← Proto-Celtic *dubnos (inherited)

← Proto-Indo-European *dʰewbʰ- (root)

← Proto-Indo-European *dʰubʰnós (inherited)

← Middle Welsh dwvyn (inherited)

→ English deep (cognate)

→ Manx dowan (cognate)

→ Polish dziupla (cognate)

→ Old Irish domun (cognate)