in esse

from The Collaborative International Dictionary of English v.0.48

In esse \In` es"se\ [L.]
   In being; actually existing; -- distinguished from {in
   posse}, or {in potentia}, which denote that a thing is not,
   but may be.
   [1913 Webster]

from Bouvier's Law Dictionary, Revised 6th Ed (1856)

IN ESSE. In being. A thing in existence. It is used in opposition to in 
posse. A child in ventre sa mere is a thing in posse; after he is born, he 
is in esse. Vide 1 Supp. to Ves. jr. 466; 2 Suppl. to Ves. jr. 155, 191. 
Vide Posse.

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