E2D2
Definition — Part II
Latin
Ad essentiam alicujus rei id pertinere dico quo dato res necessario ponitur et quo sublato res necessario tollitur; vel id sine quo res et vice versa id quod sine re nec esse nec concipi potest.
English (Elwes 1883)
I consider as belonging to the essence of a thing that, which being given, the thing is necessarily given also, and, which being removed, the thing is necessarily removed also; in other words, that without which the thing, and which itself without the thing, can neither be nor be conceived.
Modern English
I say that something belongs to the essence of a thing if, given that thing, the essence is necessarily posited, and if, removed, the essence is necessarily removed, in other words, that without which the thing can neither exist nor be conceived, and which in turn can neither exist nor be conceived without the thing.