monster vs monstrosity

monster and monstrosity both are nouns.

Word	Noun	Adjective	Verb	Adverb
monster	Yes	No	No	No
monstrosity	Yes	No	No	No

As nouns, monster and monstrosity are synonyms defined as:

monster and monstrosity: a person or animal that is markedly unusual or deformed

Other synonyms of monster include freak, lusus naturae.

monster (noun)	monstrosity (noun)
(medicine) a grossly malformed and usually nonviable fetus	something hideous or frightful
a cruel wicked and inhuman person	a person or animal that is markedly unusual or deformed
a person or animal that is markedly unusual or deformed
an imaginary creature usually having various human and animal parts
someone that is abnormally large and powerful