The Collaborative International Dictionary of English v.0.48:

Zest \Zest\ (z[e^]st), n. [F. zeste, probably fr. L. schistos
   split, cleft, divided, Gr. ?, from ? to split, cleave. Cf.
   Schism.]
   [1913 Webster]
   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.
      [1913 Webster]

   2. Hence, something that gives or enhances a pleasant taste,
      or the taste itself; an appetizer; also, keen enjoyment;
      relish; gusto.
      [1913 Webster]

            Almighty Vanity! to thee they owe
            Their zest of pleasure, and their balm of woe.
                                                  --Young.
      [1913 Webster]

            Liberality of disposition and conduct gives the
            highest zest and relish to social intercourse.
                                                  --Gogan.
      [1913 Webster]

   3. The woody, thick skin inclosing the kernel of a walnut.
      [Obs.]
      [1913 Webster]

The Collaborative International Dictionary of English v.0.48:

Zest \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.
      [1913 Webster]

   2. To give a relish or flavor to; to heighten the taste or
      relish of; as, to zest wine. --Gibber.
      [1913 Webster]

WordNet (r) 3.0 (2006):

zest
    n 1: vigorous and enthusiastic enjoyment [syn: gusto,
         relish, zest, zestfulness]
    2: a tart spicy quality [syn: nip, piquance, piquancy,
       piquantness, tang, tanginess, zest]
    v 1: add herbs or spices to [syn: zest, spice, spice up]

Moby Thesaurus II by Grady Ward, 1.0:

139 Moby Thesaurus words for "zest":
   activity, alacrity, amusement, animal pleasure, animal spirits,
   animation, anxiety, anxiousness, appetite, ardor, avidity,
   avidness, bite, bliss, bodily pleasure, breathless impatience,
   brio, briskness, capersomeness, carnal delight, cheerful readiness,
   coltishness, comfort, content, contentment, coziness,
   creature comforts, delectation, delight, eagerness, ease, ecstasy,
   edge, elan, elation, endpleasure, enjoyment, entertainment,
   enthusiasm, esprit, euphoria, exuberance, fervor, flavor,
   forepleasure, forwardness, friskiness, frolicsomeness, fruition,
   fun, gaiety, gamesomeness, gayness, ginger, glow, gratification,
   great satisfaction, gust, gusto, guts, heart, heartiness,
   hearty enjoyment, hotness, hunger, impatience, impetuosity,
   impetus, intellectual pleasure, interest, joie de vivre,
   keen desire, keen pleasure, keenness, kick, kicks, life,
   liveliness, lustiness, luxury, mettle, nip, nippiness, palate,
   passion, pepper, pepperiness, perkiness, pertness,
   physical pleasure, piquancy, piss and vinegar, playfulness,
   pleasure, promptness, punch, pungency, quickness, quiet pleasure,
   raciness, readiness, relish, robustness, rollicksomeness,
   rompishness, satisfaction, savor, self-gratification,
   self-indulgence, sensual pleasure, sensuous pleasure,
   sexual pleasure, skittishness, snap, snappiness, spice, spiciness,
   spirit, spiritedness, spirits, sportiveness, sprightliness,
   sweetness of life, tang, tanginess, thirst, titillation, verve,
   vigor, vim, vitality, vivacity, voluptuousness, warmth, well-being,
   zeal, zestfulness, zing, zip



The Free On-line Dictionary of Computing (30 December 2018):

ZEST

   An object-oriented extension of Z.

   ["Object Orientation in Z", S. Stepney et al eds, Springer
   1992].