lymphocyte vs white blood cell

lymphocyte and white blood cell both are nouns.

Word	Noun	Adjective	Verb	Adverb
lymphocyte	Yes	No	No	No
white blood cell	Yes	No	No	No

As nouns, white blood cell is a hypernym of lymphocyte; that is, white blood cell is a word with a broader meaning than lymphocyte:

lymphocyte: an agranulocytic leukocyte that normally makes up a quarter of the white blood cell count but increases in the presence of infection
white blood cell: blood cells that engulf and digest bacteria and fungi; an important part of the body's defense system

Other hypernyms of lymphocyte include leucocyte, leukocyte, WBC, white blood corpuscle, white cell, white corpuscle.

lymphocyte (noun)	white blood cell (noun)
an agranulocytic leukocyte that normally makes up a quarter of the white blood cell count but increases in the presence of infection	blood cells that engulf and digest bacteria and fungi; an important part of the body's defense system