(from esse, to be), that which constitutes the particular nature of a being or substance, or of a genus, and which distinguishes it from all others. Locke makes a distinction between nominal and real essence. The nominal essence, for example, of gold, is that complex idea expressed by gold; and its real essence is the constitution of its insensible parts, on which its properties depend, and which is unknown to us.

Essence is also used to denote the predominant qualities of any plant or drug extracted, refined, or rectified from grosser matter; or, more strictly, a volatile essential oil.

ESSENCE D'Orient, a pearly-looking substance, employed in the manufacture of artificial pearls. It is procured chiefly from the scales of the blay or bleak, a fish of the genus Cyprinus, and is prepared by the simple process of steeping the scales in water, and rubbing them with the hands until the glistening matter is separated. This is again washed, and then thrown upon a sieve, that the moisture may drain off. This substance, while in a viscid state, readily putrefies; but this tendency may be counteracted by liquor ammoniac, which coagulates the mucilaginous matter.