WordNet sense 1 (a blood group antigen possessed by Rh-positive people; if an Rh-negative person receives a blood transfusion from an Rh-positive person it can result in hemolysis and anemia):

rhesus factor, Rh factor

WordNet sense 2 (a white hard metallic element that is one of the platinum group and is found in platinum ores; used in alloys with platinum):

rhodium

WordNet sense 3 (any of several hormones produced in the hypothalamus and carried by a vein to the anterior pituitary gland where they stimulate the release of anterior pituitary hormones; each of these hormones causes the anterior pituitary to secrete a specific hormone):

releasing hormone, releasing factor, hypothalamic releasing factor, hypothalamic releasing hormone