Sentence:  <WSD>Cobs</WSD> were usually irregularly shaped. They were a means to account for a specific amount of silver in a coin that could be used for commerce. 
Meaning of the word marked with <WSD> tags:  Any of the gold and silver coins that were minted in the Spanish Empire and valued in reales or escudos, such as the piece of eight—especially those which were crudely struck and irregularly shaped.