Surely 'having fun' is what the French call 'joie de vivre'. the joy of living. Definitions of 'joie de vivre, to me defien fun.
a delight in being alive; keen, carefree enjoyment of living.
a cheerful enjoyment of life, an exultation of spirit, and general happiness. It "can be a joy of conversation, joy of eating, joy of anything one might do… And joie de vivre may be seen as a joy of everything, a comprehensive joy, a philosophy of life,
Aren't those definitions of joi de vivre also a definition of fun?
We love spa days, not the one with lots of treatments but spas with lots of ways of enjoying water with hot pools, coldpools, jacuzzis, saunas, and many other water delights. We love it and have lots of fun, especially if our DD or DGD can join us.
It was the same when we ran an antiques stall, we had great fun going to auctions and hunting stock out and also great fun at the antique fairs we did, we usually had outside pitches and met so many people, helped each other, and sold to each other.
After a day at a spa or after a good auction or sale, one was buzzing, cheerful, laughing and saying what fun we had had.