E. Cobham Brewer 18101897. Dictionary of Phrase and Fable. 1898.
A rich heiress in The Merchant of Venice, in love with Bassanio. Her father had ordained that three caskets should be offered to all who sought her handone of gold, one of silver, and one of leadwith this proviso: he only who selected the casket which contained the portrait of the lady should possess her hand and fortune. (Shakespeare.)