boyne(n = noun.act) battle of boyne - a battle in the War of the Grand Alliance in Ireland in 1690; William III defeated the deposed James II and so ended the Catholicism that had been reintroduced in England by the Stuarts;
a battle in the War of the Grand Alliance in Ireland in 1690, where William III of England defeated the deposed James II and so ended Stuart Catholicism in England. [WordNet 1.5]