a form of anemia characterized by a gradual reduction in the number of the red blood cells, gastrointestinal and nervous disturbances, etc., due to a deficiency of vitamin B
See pernicious anemia in American Heritage Dictionary 4
noun
A severe anemia most often affecting older adults, caused by failure of the stomach to absorb vitamin B12 and characterized by abnormally large red blood cells, gastrointestinal disturbances, and lesions of the spinal cord.