Breton laou

← Proto-Celtic *luwā (inherited)

← Welsh llau (cognate)

← English louse (cognate)

← Proto-Indo-European *lewH- (root)

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

← Cornish low (cognate)

← Middle Breton lou (inherited)

→ Welsh llau (cognate)

→ Norwegian Nynorsk lus (cognate)