The Collaborative International Dictionary
In esse
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.
Wiktionary
in esse
a. in being, in actuality, have actual existence, (contradistinguished by ''in posse'', compare ''in potentia'') adv. in being, in actuality, having actual existence, (contradistinguished by ''in posse'', compare ''in potentia'')