The kingdom of Queen Quintessence in the famous satirical romance of Rabelais called the History of Gargantua and Pantagruel'. Pantagruel and his companions went thither in search of the Holy Bottle. It may be called the city of speculative science.
The word is used to express the realisation of a beau ideal. Lovers have preconceived notions of human perfections, and imagine that they see the realities in the person beloved, who is the entelechy of their beau ideal.
O lumiere! enrichie D'un feu divin, qui m'ard si vivement, Pour me donner l'etre et le movement, Etes-vous pas ma seul entelechie.
Ronsard: sonnet 68 (1524-35).
Source: Dictionary of Phrase and Fable, E. Cobham Brewer, 1894