monster vs demon

monster and demon both are nouns.

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

As nouns, monster and demon are synonyms defined as:

Other synonyms of monster include devil, fiend, ogre.

monster (noun)	demon (noun)
(medicine) a grossly malformed and usually nonviable fetus	an evil supernatural being
a cruel wicked and inhuman person	a cruel wicked and inhuman person
a person or animal that is markedly unusual or deformed	someone extremely diligent or skillful
an imaginary creature usually having various human and animal parts
someone that is abnormally large and powerful