Full Idea
By 'attribute' I understand that which the intellect perceives of substance, as if constituting its essence.
Gist of Idea
An 'attribute' is what the intellect takes as constituting an essence
Source
Baruch de Spinoza (The Ethics [1675], I Def 4)
Book Reference
Spinoza,Benedict de: 'Ethics', ed/tr. White,WH/Stirling,AH [Wordsworth 2001], p.3
A Reaction
Note that we would call these 'properties', but Spinoza has a word reserved for the properties of essences. He also has 'modes' of a thing, which are different.
Related Idea
Idea 17171 A 'mode' is an aspect of a substance, and conceived through that substance [Spinoza]