Kay Redfield Jamison defines “exuberance”:
“Exuberance,” derived from the Latin exuberance—ex, “out of,” + uberare, “to be fruitful, to be abundant”—is at its core a concept of fertility. Exuberance in nature is defined by lush, profuse, riotous growth; it is an overflowing, opulent, and copious abundance…A fruitful outcome of an alchemy experiment, for instance, was characterized as “exuberated earth” in 1471, according to the Oxford English Dictionary…Kay Redfield Jamison. Exuberance: The Passion for Life. New York: Vintage Books, 2004. p. 24.
“Enthusiasm” is different. Instead of fertility and abundance, it’s about finding some inspiration, sublime grandeur, or joy within.
The Greeks understood the mysterious power of the hidden side of things. They bequeathed to us one of the most beautiful words in our language—the word ‘enthusiasm’—en theos—a god within. The grandeur of human actions is measured by the inspiration from which they spring. Happy is he who bears a god within, and who obeys it.Kay Redfield Jamison. Exuberance: The Passion for Life. New York: Vintage Books, 2004. p. 5.