ultimo vs past

ultimo is not a noun while past is a noun.

Word	Noun	Adjective	Verb	Adverb
ultimo	No	Yes	No	No
past	Yes	Yes	No	Yes

ultimo (noun)	past (noun)
	a verb tense that expresses actions or states in the past
	the time that has elapsed
	a earlier period in someone's life (especially one that they have reason to keep secret)

ultimo (adjective)	past (adjective)
in or of the month preceding the present one	earlier than the present time; no longer current
	of a person who has held and relinquished a position or office

ultimo (adverb)	past (adverb)
	so as to pass a given point