The Collaborative International Dictionary of English v.0.48:
Quintessential \Quin`tes*sen"tial\, a. Of the nature of a quintessence; purest; most characteristic. "Quintessential extract of mediocrity." --G. Eliot. [1913 Webster] QuintetWordNet (r) 3.0 (2006):
quintessential adj 1: representing the perfect example of a class or quality