fun vs diversion

fun and diversion both are nouns.

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

As nouns, diversion is a hypernym of fun; that is, diversion is a word with a broader meaning than fun:

Other hypernyms of fun include recreation.

fun (noun)	diversion (noun)
activities that are enjoyable or amusing	an activity that diverts or amuses or stimulates
violent and excited activity	a turning aside (of your course or attention or concern)
a disposition to find (or make) causes for amusement	an attack calculated to draw enemy defense away from the point of the principal attack
verbal wit or mockery (often at another's expense but not to be taken seriously)