The Collaborative International Dictionary of English v.0.48:

Essence \Es"sence\, n. [F. essence, L. essentia, formed as if
   fr. a p. pr. of esse to be. See Is, and cf. Entity.]
   1. The constituent elementary notions which constitute a
      complex notion, and must be enumerated to define it;
      sometimes called the nominal essence.
      [1913 Webster]

   2. The constituent quality or qualities which belong to any
      object, or class of objects, or on which they depend for
      being what they are (distinguished as real essence); the
      real being, divested of all logical accidents; that
      quality which constitutes or marks the true nature of
      anything; distinctive character; hence, virtue or quality
      of a thing, separated from its grosser parts.
      [1913 Webster]

            The laws are at present, both in form and essence,
            the greatest curse that society labors under.
                                                  --Landor.
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            Gifts and alms are the expressions, not the essence
            of this virtue [charity].             --Addison.
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            The essence of Addison's humor is irony.
                                                  --Courthope.
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   3. Constituent substance.
      [1913 Webster]

            And uncompounded is their essence pure. --Milton.
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   4. A being; esp., a purely spiritual being.
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            As far as gods and heavenly essences
            Can perish.                           --Milton.
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            He had been indulging in fanciful speculations on
            spiritual essences, until . . . he had and ideal
            world of his own around him.          --W. Irving.
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   5. The predominant qualities or virtues of a plant or drug,
      extracted and refined from grosser matter; or, more
      strictly, the solution in spirits of wine of a volatile or
      essential oil; as, the essence of mint, and the like.
      [1913 Webster]

            The . . . word essence . . . scarcely underwent a
            more complete transformation when from being the
            abstract of the verb "to be," it came to denote
            something sufficiently concrete to be inclosed in a
            glass bottle.                         --J. S. Mill.
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   6. Perfume; odor; scent; or the volatile matter constituting
      perfume.
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            Nor let the essences exhale.          --Pope.
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The Collaborative International Dictionary of English v.0.48:

Essence \Es"sence\, v. t. [imp. & p. p. Essenced; p. pr. & vb.
   n. Essencing.]
   To perfume; to scent. "Essenced fops." --Addison.
   [1913 Webster]

WordNet (r) 3.0 (2006):

essence
    n 1: the choicest or most essential or most vital part of some
         idea or experience; "the gist of the prosecutor's
         argument"; "the heart and soul of the Republican Party";
         "the nub of the story" [syn: kernel, substance, core,
         center, centre, essence, gist, heart, heart and
         soul, inwardness, marrow, meat, nub, pith,
         sum, nitty-gritty]
    2: any substance possessing to a high degree the predominant
       properties of a plant or drug or other natural product from
       which it is extracted
    3: the central meaning or theme of a speech or literary work
       [syn: effect, essence, burden, core, gist]
    4: a toiletry that emits and diffuses a fragrant odor [syn:
       perfume, essence]

Moby Thesaurus II by Grady Ward, 1.0:

289 Moby Thesaurus words for "essence":
   affective meaning, ambergris, ambrosia, aroma, aromatic,
   aromatic gum, aromatic water, artifact, aspect, at bottom, attar,
   attar of roses, attribute, au fond, axiom, balm, balm of Gilead,
   balsam, basically, basis, bay oil, be-all and end-all, bearing,
   being, bench mark, bergamot oil, best part, better part, body,
   bottom, brainchild, breath, bulk, burden, cardinal point, case,
   center, champaca oil, chapter, chief thing, child, civet, climax,
   coinage, coloring, composition, concentrate, concentration,
   concern, concoction, connotation, consequence, core, cornerstone,
   creation, creature, crisis, critical, critical point,
   crowning achievement, crucial, crux, decoction, definite odor,
   denotation, detectable odor, distillate, distillation, drift,
   effect, effluvium, element, elixir, emanation, end product, ens,
   entity, esse, essential, essential matter, essential oil,
   essentiality, essentially, exhalation, existence, extension,
   extract, extraction, fabric, fiber, fixative, flavor, flower,
   focus, focus of attention, focus of interest, force, form,
   fragrance, fruit, fume, fundamental, fundamentally, generality,
   gist, grammatical meaning, gravamen, great point, handiwork, head,
   heading, heart, heliotrope, high point, hypostasis, idea, impact,
   implication, import, important, important thing, in effect,
   in essence, indispensable, infusion, inner essence, intension,
   invention, inwardness, issue, jasmine oil, kernel, keystone,
   landmark, lavender oil, lexical meaning, life, literal meaning,
   living issue, main body, main point, main thing, major part,
   majority, manufacture, marrow, mass, masterpiece, masterwork,
   material, material point, materiality, materially, matter,
   matter in hand, meaning, meat, medium, milestone, mintage, most,
   motif, motive, musk, myrcia oil, myrrh, nature, new mintage, nub,
   nubbin, nucleus, nuts and bolts, occurrence, odor, of the essence,
   offspring, opera, opus, opuscule, origination, outcome, outgrowth,
   overtone, parfum, perfume, perfumery, pertinence, pith, pivot,
   plurality, point, point at issue, point in question, postulate,
   practical consequence, presence, principle, problem, product,
   production, property, purification, purport, quality, question,
   quid, quiddity, quintessence, quintessential, range of meaning,
   real issue, real meaning, recap, recapitulation, redolence,
   reference, referent, refinement, relation, relevance, requisite,
   result, resume, rock bottom, root, rose oil, rubric, run-through,
   rundown, salient point, sap, savor, scent, scope, semantic cluster,
   semantic field, sense, significance, signification, significatum,
   signifie, sine qua non, smell, soul, span of meaning, spirit,
   spoor, stench, structural meaning, stuff, subject, subject matter,
   subject of thought, subsistence, substance, substantiality,
   substantially, substantive point, subtle odor, sum,
   sum and substance, summary, summation, symbolic meaning, tenor,
   text, texture, the bottom line, the nitty-gritty, the point, theme,
   thrust, timber, tincture, topic, totality of associations, trace,
   trail, transferred meaning, turning point, unadorned meaning,
   undertone, value, virtuality, virtually, vital, volatile oil,
   whiff, work