Welsh blwyddyn

← Breton blizen (cognate)

← Proto-Celtic *blēdanī (inherited)

← Proto-Celtic *blēdon (mention)

← Welsh blwydd (cognate)

← Cornish blydhen (cognate)

← Old Welsh bloidin (inherited)

← Old Irish blíadain (cognate)

→ Breton bloaz (mention)

→ Welsh blynyddol (affix)

→ Welsh blynyddoedd (affix)

→ Welsh blwyddyn golau (affix)

→ Old Irish blíadain (cognate)