myelocyte vs white blood cell

myelocyte and white blood cell both are nouns.

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

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

myelocyte: an immature leukocyte normally found in bone marrow
white blood cell: blood cells that engulf and digest bacteria and fungi; an important part of the body's defense system

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

myelocyte (noun)	white blood cell (noun)
an immature leukocyte normally found in bone marrow	blood cells that engulf and digest bacteria and fungi; an important part of the body's defense system