Polignac, Melchior de (mĕlkyôrˈ də pôlēnyäkˈ) [key], 1661–1742, French diplomat, churchman, and author, cardinal of the Roman Catholic Church. As ambassador to Poland he directed (1697) the unsuccessful candidacy of François Louis de Conti for the Polish crown. He was one of the negotiators of the Peace of Utrecht (1713–14). After being in disgrace during the regency of Philippe II d'Orléans, he served as ambassador to the Holy See. His Anti-Lucretius (1745, in Latin; tr. 1757) is a philosophical poem attacking materialism from the Cartesian viewpoint.