passe vs ex

passe is not a noun while ex is a noun.

Word	Noun	Adjective	Verb	Adverb
passe	No	Yes	No	No
ex	Yes	Yes	No	No

As adjectives, passe and ex are synonyms defined as:

Other synonyms of passe include antique, demode, old-fashioned, old-hat, outmoded, passee.

passe (noun)	ex (noun)
	the 24th letter of the Roman alphabet
	a woman who was formerly a particular man's wife
	a man who was formerly a certain woman's husband

passe (adjective)	ex (adjective)
out of fashion	out of fashion