E. Cobham Brewer 18101897. Dictionary of Phrase and Fable. 1898.
The bandit-captain, Duke of Segorbia and Cardona, Lord of Aragon, and Count of Ernani, in love with Elvira, who is betrothed to Don Ruy Gomez de Silva, an old Spanish grandee, whom she detests. Charles V. of Spain also loves her, and tries to win her. Silva, finding that the king has been tampering with his betrothed, joins the league of Ernani against the king. The king in concealment overhears the plotters, and, at a given signal, they are arrested by his guards, but, at the intercession of Elvira, are pardoned and set free. Ernani is on the point of marrying Elvira, when a horn is heard. This horn Ernani had given to Silva when he joined the league, saying, Sound but this horn, and at that moment Ernani will cease to live. Silva insists on the fulfilment of the compact, and Ernani stabs himself. (Verdis opera of Ernani.)