Escuage
Black's Law Dictionary · Henry Campbell Black, M.A. · 1910
Black's Law Dictionary
Service of the shield. One of the varieties of tenure in knight's service, the duty imposed being that of accompanying the king to the wars for forty days, at the tenant's own charge, or sending a substitute. In later times, this servico was commuted for a certain payment in money, which was then called "escuage certain."
See 2 Bl. Comm. 74, 75.