fun vs pertness

fun and pertness both are nouns.

Word	Noun	Adjective	Verb	Adverb
fun	Yes	No	No	No
pertness	Yes	No	No	No

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

fun (noun)	pertness (noun)
activities that are enjoyable or amusing	inappropriate playfulness
violent and excited activity	quality of being lively and confident
a disposition to find (or make) causes for amusement
verbal wit or mockery (often at another's expense but not to be taken seriously)