Source : Webster's Revised Unabridged Dictionary (1913)

Bonanza \Bo*nan"za\, n. [Sp., prop. calm., fair weather,
   prosperity, fr. L. bonus good.]
   In mining, a rich mine or vein of silver or gold; hence,
   anything which is a mine of wealth or yields a large income.
   [Colloq. U. S.]

Source : WordNet®

bonanza
     n 1: an especially rich vein of precious ore
     2: a sudden happening that brings good fortune (as a sudden
        opportunity to make money); "the demand for testing has
        created a boom for those unregulated laboratories where
        boxes of specimen jars are processed lik an assembly line"
        [syn: {boom}, {gold rush}, {gravy}, {godsend}, {manna from
        heaven}, {windfall}, {bunce}]