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Webster 1913 Edition

Adj.

Of the nature of a quintessence; purest; most characteristic.

“Quintessential extract of mediocrity.”

G. Eliot.

Adj.

Consisting of quintessence.

quintessential ‎(comparative more quintessential, superlative most quintessential)

Of the nature of a quintessence (in all senses); ultimate.
- 2014 May 6, Nicholas Shakespeare, “Twin Tracks by Roger Bannister, review: Roger Bannister's memoir of a life in athletics recalls the moment 60 years ago when he broke the four-minute mile [print version: The quiet Englishman, 10 May 2014, p. R26]”, in The Daily Telegraph (Review):
  Twin Tracks is the old-fashioned autobiography of a quintessential Englishman, evocative of an age when you took halibut oil for rickets and sportsmen were amateurs who trained in their lunch breaks.

of the nature of a quintessence