Essentially, quintessential has a quintessentially interesting etymology. When it was first borrowed around the year 1600, it meant something more like "purest" rather than its current meaning of "exemplification". Through Middle French, this comes the Medieval Latin phrase quinta essentia, which meant "fifth essence"- the equivalent of the "fifth element" that we know so well from pop culture. This is because, in addition to earth, air, fire, and water, there was thought to be a fifth element which was purer than all the rest, and, therefore, quintessential. Quinta comes from quinque, which meant "five" and in turn derived from the Proto-Indo-European reconstruction penke, which also meant "five" but was probably related to words meaning "fist" and/or "fingers". Meanwhile, essentia was created off the verb esse, "to be". This is thought to be from PIE es, with the same definition. A nice, interesting etymology... until the Fire Nation attacked.
Adam Aleksic, a rising sophomore studying linguistics and government at Harvard University, has been described as the internet's sixth most famous etymologist. He also has disturbing interests in politics, vexillology, geography, board games, conlanging, and law.