Zest, n.
Etymology: [F. zeste, probably fr. L. schistos split, cleft, divided, Gr. Schism.]
1. A piece of orange or lemon peel, or the aromatic oil which may be squeezed from such peel, used to give flavor to liquor, etc.
2. Hence, something that gives or enhances a pleasant taste, or the taste itself; an appetizer; also, keen enjoyment; relish; gusto. Almighty Vanity! to thee they owe Their zest of pleasure, and their balm of woe. Young. Liberality of disposition and conduct gives the highest zest and relish to social intercourse. Gogan.
3. The woody, thick skin inclosing the kernel of a walnut. [Obs.]
1 other Webster entry under this spelling
Zest, v. t. [imp. & p. p. Zested; p. pr. & vb. n. Zesting.]
1. To cut into thin slips, as the peel of an orange, lemon, etc.; to squeeze, as peel, over the surface of anything.
2. To give a relish or flavor to; to heighten the taste or relish of; as, to zest wine. Gibber.
Shades of meaning
Fernald has no entry of its own for zest; he lists it under appetite.
He lists it without comment; the entries above explain its neighbors.