The ancient greeks recognised four elements, fire, air, water, and earth. The pythagoreans added a fifth and called it nether, the fifth essence, which they said flew upward at creation and out of it the stars were made. The alchemists sometimes considered alcohol, or the ferment oils, as the fifth essence.
2. Hence: An extract from anything, containing its rarest virtue, or most subtle and essential constituent in a small quantity; pure or concentrated essence. Let there be light, said god; and forthwith light ethereal, first of things, quintessence pure, Sprung from the deep. (milton)
Origin: F, fr. L. Quinta essentia fifth essence. See Quint, and Essence.