zoology vs malacology

zoology and malacology both are nouns.

Word	Noun	Adjective	Verb	Adverb
zoology	Yes	No	No	No
malacology	Yes	No	No	No

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

zoology: the branch of biology that studies animals
malacology: the branch of zoology that studies the structure and behavior of mollusks

zoology (noun)	malacology (noun)
the branch of biology that studies animals	the branch of zoology that studies the structure and behavior of mollusks
all the animal life in a particular region or period