nihilism vs ism

nihilism and ism both are nouns.

Word	Noun	Adjective	Verb	Adverb
nihilism	Yes	No	No	No
ism	Yes	No	No	No

As nouns, ism is a hypernym of nihilism; that is, ism is a word with a broader meaning than nihilism:

nihilism: a revolutionary doctrine that advocates destruction of the social system for its own sake
ism: a belief (or system of beliefs) accepted as authoritative by some group or school

Other hypernyms of nihilism include doctrine, philosophical system, philosophy, school of thought.

nihilism (noun)	ism (noun)
a revolutionary doctrine that advocates destruction of the social system for its own sake	a belief (or system of beliefs) accepted as authoritative by some group or school
complete denial of all established authority and institutions
the delusion that things (or everything, including the self) do not exist; a sense that everything is unreal