trivial vs petty

trivial is not a noun while petty is a noun.

Word	Noun	Adjective	Verb	Adverb
trivial	No	Yes	No	No
petty	Yes	Yes	No	No

As adjectives, trivial and petty are synonyms defined as:

Other synonyms of trivial include fiddling, footling, lilliputian, little, niggling, picayune, piddling, piffling.

trivial (noun)	petty (noun)
	larceny of property having a value less than some amount (the amount varies by locale)

trivial (adjective)	petty (adjective)
concerned with trivialities	inferior in rank or status
of little substance or significance	contemptibly narrow in outlook
(informal) small and of little importance	(informal) small and of little importance