E. Cobham Brewer 18101897. Dictionary of Phrase and Fable. 1898.
A sword of ice-brook temper. Of the very best quality. The Spaniards used to plunge their swords and other weapons, while hot from the forge, into the brook Salo [Xalon], near Bilbilis, in Celtiberia, to harden them. The water of this brook is very cold.