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Full Idea
The definition of a thing should be such that all the properties of that thing, in so far as it is considered by itself, and not in conjunction with other things, can be deduced from it.
Gist of Idea
All the intrinsic properties of a thing should be deducible from its definition
Source
Baruch de Spinoza (Improvement of Understanding [1675], p.35), quoted by E.J. Lowe - What is the Source of Knowledge of Modal Truths? 6
Book Ref
-: 'Mind' [-], p.20
A Reaction
This is exactly what Locke requires of a real essence (though he is pessimistic about ever achieving it). Spinoza is talking of an Aristotelian real definition, which may be complex, and not a lexicographer's short verbal explication.