Best definition
an activity deemed as so either amazing, incredible, joyful, pleasureable, fantastic, or epic as to have the appearance of fun

yet deserving of a title fusing ‘wonderful’ with said action being ‘fun’ ; epic

dude: hey baby what do you think of having sex?

chick: you mean wonderfun? nothin better 😉
Wonderfun: define #2
When something is wonderful and funny or fun its wonderfun
OMG that was totally wonderfun, lets do it again.