c.1430, in ancient and medieval philosophy, "pure essence, substance of which the heavenly bodies are composed," lit. "fifth essence," from M.Fr.
quinte essence (14c.), from M.L.
quinta essentia, from L.
quinta, fem. of
quintus "fifth" +
essentia (see
essence). Loan-translation of Gk.
pempte ousia, the "ether" added by Aristotle to the four known elements (water, earth, fire, air) and said to permeate all things. Its extraction was one of the chief goals of alchemy. Sense of "purest essence" (of a situation, character, etc.) is first recorded 1570;
quintessential (n.) is from 1899, in this sense.
[kwin-tes-uh
ns] 
Word Origin & History