Welsh dwy

← Proto-Celtic *dwī (inherited)

← Proto-Celtic *dwau (mention)

← Proto-Indo-European *dwih₂ (inherited)

← Proto-Indo-European *dwóh₁ (mention)

→ Welsh dwywaith (affix)

→ Welsh tradwy (affix)

→ Welsh un deg dwy (compound)

→ Welsh dwy ar bymtheg (compound)

→ Welsh dau ddeg dwy (compound)

→ Welsh dwyflwydd (compound)