WordNet (r) 3.0 (2006):

leukocyte
    n 1: blood cells that engulf and digest bacteria and fungi; an
         important part of the body's defense system [syn:
         leukocyte, leucocyte, white blood cell, white cell,
         white blood corpuscle, white corpuscle, WBC]

Moby Thesaurus II by Grady Ward, 1.0:

52 Moby Thesaurus words for "leukocyte":
   Rh factor, Rh-negative, Rh-positive, Rh-type, Rhesus factor,
   antibody, antigen, arterial blood, blood, blood bank, blood cell,
   blood count, blood donor, blood donor center, blood group,
   blood grouping, blood picture, blood platelet, blood pressure,
   blood serum, blood substitute, bloodmobile, bloodstream,
   circulation, clinical dextran, dextran, erythrocyte, globulin,
   gore, grume, hematics, hematologist, hematology, hematoscope,
   hematoscopy, hemocyte, hemoglobin, hemometer, humor, ichor,
   isoantibody, lifeblood, neutrophil, opsonin, phagocyte, plasma,
   plasma substitute, red corpuscle, serum, type O, venous blood,
   white corpuscle