Definitions for factor ix
Christmas factor, factor IX(noun)
coagulation factor whose absence is associated with hemophilia B
U.S. National Library of Medicine
Storage-stable blood coagulation factor acting in the intrinsic pathway. Its activated form, IXa, forms a complex with factor VIII and calcium on platelet factor 3 to activate factor X to Xa. Deficiency of factor IX results in HEMOPHILIA B (Christmas Disease).