megaloblast

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

• noun An abnormally large nucleated red blood cell found especially in people having pernicious anemia or certain vitamin deficiencies.

from The Century Dictionary.

• noun A large nucleate cell found in the bone-marrow in the embryo: also a megalocyte, or large red blood-corpuscle occurring in certain forms of anemia in extra-uterine life.

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

• noun An abnormally large red blood cell associated with pernicious anemia and with folic acid deficiency

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

• noun abnormally large red blood cell present in pernicious anemia and folic acid deficiency