Welsh tair

← Proto-Celtic *tisres (inherited)

← Proto-Celtic *trīs (mention)

← Proto-Indo-European *tisres (inherited)

← Proto-Indo-European *tréyes (mention)

→ Welsh teirgwaith (compound)

→ Welsh tair ar ddeg (compound)

→ Welsh teires (compound)

→ Welsh un deg tair (compound)

→ Welsh dau ddeg tair (compound)