piece of eight

Noun

1. peso, a silver coin, that was minted in Spain and its colonies from the end of 15th century, equal to eight reales (hence the name).
   • It was a long, difficult business, for the coins were of all countries and sizes — doubloons, and louis d'ors, and guineas, and pieces of eight, and I know not what besides, all shaken together at random. — Robert Louis Stevenson, "Treasure Island".