Welsh trwy

← Proto-Brythonic *truɨ (inherited)

← Proto-Celtic *trē (inherited)

← Proto-Indo-European *terh₂- (derived)

← Old Welsh troi (inherited)

← Middle Welsh trwy (inherited)

→ Irish trí (cognate)

→ Scottish Gaelic tre (cognate)

→ Middle Irish tre (cognate)

→ Old Irish tre (cognate)