biology vs cytology

biology and cytology both are nouns.

Word	Noun	Adjective	Verb	Adverb
biology	Yes	No	No	No
cytology	Yes	No	No	No

As nouns, cytology is a hyponym of biology; that is, cytology is a word with a more specific, narrower meaning than biology:

biology: the science that studies living organisms
cytology: the branch of biology that studies the structure and function of cells

biology (noun)	cytology (noun)
the science that studies living organisms	the branch of biology that studies the structure and function of cells
all the plant and animal life of a particular region
characteristic life processes and phenomena of living organisms