n.1 the most essential part of any substance; a refined extract.
2 (usu. foll. by of) the purest and most perfect, or most typical, form, manifestation, or embodiment of some quality or class.
3 (in Ancient Philosophy) a fifth substance (beside the four elements) forming heavenly bodies and pervading all things.
Derivatives:
quintessential adj. quintessentially adv.
Etymology: ME (in sense 3) f. F f. med.L quinta essentia fifth ESSENCE