Scutage

Scutage was a medieval English tax levied on holders of a knight's fee under the feudal land tenure of knight-service. Under feudalism the king, through his vassals, provided land to knights for their support. The knights owed the king military service in return. The knights were allowed to "buy out" of the military service by paying scutage (a term derived from Latin scutum, "shield").

As time passed the kings began to impose a scutage on holders of knight's fees, whether or not the holder was actually a knight.