lymphocyte

n. almost colorless cell which is formed in the lymphoid tissue and is active in the development of the body's immunity

A lymphocyte is a type of  white blood cell in the vertebrate immune system. By their appearance under the light microscope, there are two broad categories of lymphocytes, namely the large granular lymphocytes and the small lymphocytes. Functionally distinct subsets of lymphocytes correlate with their appearance. Most, but not all large granular lymphocytes are more commonly known as the natural killer cells (NK cells). The small lymphocytes are the T cells and B cells. Lymphocytes play an important and integral role in the body's defenses. An average human body contains about 10^12 lymphoid cells, and the lymphoid tissue as a whole represents about 2% of the total body weight.
See more at Wikipedia.org...

Noun
1. an agranulocytic leukocyte that normally makes up a quarter of the white blood cell count but increases in the presence of infection
(synonym) lymph cell
(hypernym) leukocyte, leucocyte, white blood cell, white cell, white blood corpuscle, white corpuscle, WBC
(hyponym) B cell, B lymphocyte
(part-holonym) lymphatic system, systema lymphaticum

n. lymphocyte, almost colorless cell which is formed in the lymphoid tissue and is active in the development of the body's immunity

[LIM-fo-site]
A type of white blood cell. Lymphocytes have a number of roles in the immune system, including the production of antibodies and other substances that fight infection and diseases.