pettiness vs slightness

pettiness and slightness both are nouns.

Word	Noun	Adjective	Verb	Adverb
pettiness	Yes	No	No	No
slightness	Yes	No	No	No

As nouns, pettiness and slightness are synonyms defined as:

pettiness and slightness: the quality of being unimportant and petty or frivolous

Other synonyms of pettiness include puniness, triviality.

pettiness (noun)	slightness (noun)
the quality of being unimportant and petty or frivolous	slenderness
lack of generosity in trifling matters	the property of an attractively thin person
narrowness of mind or ideas or views	the quality of being unimportant and petty or frivolous