expulsion vs ousting

expulsion and ousting both are nouns.

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

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

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

expulsion (noun)	ousting (noun)
the act of expelling or projecting or ejecting	the act of ejecting someone or forcing them out
the act of forcing out someone or something
squeezing out by applying pressure