Irish nathair

← Breton naer (cognate)

← Proto-Celtic *natrixs (inherited)

← Welsh neidr (cognate)

← English adder (cognate)

← Proto-Indo-European *nh₁trih₂ (inherited)

← Proto-Indo-European *snéh₁- (mention)

← Latin natrīx (cognate)

← Old Irish nathir (inherited)

→ Breton naer (cognate)

→ Welsh neidr (cognate)

→ Irish nathartha (affix)