Corresponding to the Italian scudo, meant originally a sheild, from the device on the coin. Similarly the Dutch employ the term Schild, the Spaniards Escudo, etc.
The silver Ecu, or Ecu Blanc, as it is frequently called, appeared under Louis XIII in 1641, and had a value of sixty Sols. There were also struck a number of sub-divisions. See Hoffmann, Les monnaies royales de France. 1878. Under Louis XV the value of the Ecu varied at three, five, and six Libres, and under Louis XVI it was made equal to the latter figure.
Source: Frey's Dictionary (American Journal of Numismatics, Vol. 50, 1916)