Eagle, the king of birds, and bird of Jove; was adopted by various nations as the emblem of dominant power, as well as of nobility and generosity; in Christian art it is the symbol of meditation, and the attribute of St. John; is represented now as fighting with a serpent, and now as drinking out of a chalice or a communion cup, to strengthen it for the fight.
Definition taken from The Nuttall Encyclopædia, edited by the Reverend James Wood (1907)
Eads, James Buchanan * Eagle, Order of the Black