Sentence:  Early in the second millennium, the spread of the money economy eroded and eventually destroyed feudalism. The moment that a peasant could sell his labor to the highest bidder, the ties that bound servant and master dissolved. [...] Not only were individuals able to buy their freedom with <WSD>coin of the realm</WSD>; at times, entire villages did so, as when the northern French city of Coucy-le-Château bought its charter of liberties from the penniless widow of the lord for 140 livres in 1197. 
Meaning of the word marked with <WSD> tags:  The legal money of a country.