past vs preterit

past and preterit both are nouns.

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

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

Other hyponyms of past include preterite, past simple, simple past.

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

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earlier than the present time; no longer current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

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