Welsh trwm

← Proto-Brythonic *trumm (inherited)

← Proto-Celtic *trummos (inherited)

→ English droumy (cognate)

→ Welsh trymhau (affix)

→ Welsh pendrwm (affix)

→ Irish trom (cognate)

→ Scottish Gaelic trom (cognate)

→ Galician trosma (cognate)

→ Manx trome (cognate)

→ Old Irish trom (cognate)