white blood cell

from The American Heritage® Dictionary of the English Language, 5th Edition.

• noun Any of various nucleated blood cells that lack hemoglobin and function in the immune system to protect against agents of infection and foreign matter. White blood cells include neutrophils, eosinophils, basophils, lymphocytes, and monocytes.

from Wiktionary, Creative Commons Attribution/Share-Alike License.

• noun hematology, cytology, immunology A type of blood cell that is involved with an immune response, or part of the immune system.

from WordNet 3.0 Copyright 2006 by Princeton University. All rights reserved.

• noun blood cells that engulf and digest bacteria and fungi; an important part of the body's defense system