expulsion vs ostracism

expulsion and ostracism both are nouns.

Word	Noun	Adjective	Verb	Adverb
expulsion	Yes	No	No	No
ostracism	Yes	No	No	No

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

Other hyponyms of expulsion include defenestration, deportation, barring, blackball, ouster, ousting.

expulsion (noun)	ostracism (noun)
the act of expelling or projecting or ejecting	the act of excluding someone from society by general consent
the act of forcing out someone or something	the state of being banished or ostracized (excluded from society by general consent)
squeezing out by applying pressure