PRINCIPLE n.
Any original inherent constituent which characterizes a substance, or gives it its essential properties, and which can usually be separated by analysis; -- applied especially to drugs, plant extracts, etc. Cathartine is the bitter, purgative principle of senna. Gregory. Bitter principle, Principle of contradiction, etc…
QUINTESSENCE n.
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.