adj. 1. the Roman number symbolizing the value thirteen. Used after a noun it may symbolize the ordinal number; as, Superbowl XIII. Syn. -- thirteen, 13. [ WordNet 1.5 ]
(n) Italian pope from 1878 to 1903 who was interested in the advancement of learning and who opened the Vatican secret archives to all scholars, Syn. Giovanni Vincenzo Pecci, Gioacchino Pecci
(n) in the clotting of blood thrombin catalyzes factor XIII into its active form (fibrinase) which causes fibrin to form a stable clot, Syn. factor XIII