quintessence

Concise Oxford English Dictionary © 2008 Oxford University Press:
quintessence /kwɪnˈtɛs(ə)ns/

▶noun

• 1 the most perfect or typical example.

  ■ a central and intrinsic aspect of something.

• 2 a refined essence or extract of a substance.

• 3 (in ancient philosophy) a fifth substance in addition to the four elements, thought to compose the heavenly bodies and pervade all things.

word history: The word quintessence comes from the medieval Latin term quinta essentia, meaning ‘fifth essence’, and denoted a fifth substance believed to exist in addition to the four elements air, earth, fire, and water. Medieval philosophers believed that this ‘fifth essence’ was the substance of which the celestial bodies were composed, and that it was present in all things.