An unlucky possession, something that brings evil to all who possess it. Harmonia was the daughter of Mars and Venus. On the day of her marriage with King Cadmos, she received a necklace which proved fatal to all who possessed it.
The collar given by Alphesibea (or Arsinoë) to her husband Alcmaeon was a like fatal gift. So were the collar and veil of Eriphyle, wife of Amphiaraos, and the Trojan horse. (See Fatal Gifts.)
Source: Dictionary of Phrase and Fable, E. Cobham Brewer, 1894