The Collaborative International Dictionary of English v.0.48:

Emptiness \Emp"ti*ness\, n. [From Empty.]
   1. The state of being empty; absence of contents; void space;
      vacuum; as, the emptiness of a vessel; emptiness of the
      stomach.
      [1913 Webster]

   2. Want of solidity or substance; unsatisfactoriness;
      inability to satisfy desire; vacuity; hollowness; as, the
      emptiness of earthly glory.
      [1913 Webster]

   3. Want of knowledge; lack of sense; vacuity of mind.
      [1913 Webster]

            Eternal smiles his emptiness betray.  --Pope.
      [1913 Webster]

            The sins of emptiness, gossip, and spite.
                                                  --Tennyson.
      [1913 Webster]

WordNet (r) 3.0 (2006):

emptiness
    n 1: the state of containing nothing [ant: fullness]
    2: having an empty stomach
    3: an empty area or space; "the huge desert voids"; "the
       emptiness of outer space"; "without their support he'll be
       ruling in a vacuum" [syn: void, vacancy, emptiness,
       vacuum]
    4: the quality of being valueless or futile; "he rejected the
       vanities of the world" [syn: vanity, emptiness]

Moby Thesaurus II by Grady Ward, 1.0:

228 Moby Thesaurus words for "emptiness":
   absence, absence of mind, absurdity, acreage, aimlessness, angst,
   anguish, anxiety, appetite, area, aridity, bareness, barrenness,
   big deal, blankness, bleakness, bloodlessness, bootlessness,
   boredom, breadth, canine appetite, casuistry, characterlessness,
   cheerlessness, colorlessness, continuum, crossed fingers,
   dead letter, deadness, deprivation, desertedness, desolateness,
   desolation, dimension, discomfort, discomposure, discontent,
   disingenuousness, dislike, dismalness, displeasure, disquiet,
   dissatisfaction, dragginess, dread, dreariness, drought, dryness,
   dullness, dustiness, effeteness, emotionlessness, empty sound,
   empty space, empty stomach, empty-headedness, ennui, etiolation,
   existential woe, expanse, expansion, expressionlessness, extension,
   extent, fatuity, fecklessness, field, flatness, flimsiness,
   foolishness, frivolity, frivolousness, fruitlessness, futility,
   galactic space, grimness, heaviness, hollow hunger, hollow mockery,
   hollowness, hunger, hungriness, idleness, impotence, inanition,
   inanity, ineffectiveness, ineffectuality, inefficacy,
   inexcitability, infinite space, inquietude, insignificance,
   insincerity, insipidity, insipidness, interstellar space, jejunity,
   jesuitry, joylessness, lack of pleasure, leadenness, levity,
   lifelessness, lightness, lowness of spirit, malaise,
   meaninglessness, measure, mental void, mere noise, mockery, nausea,
   negation, negativeness, negativity, nihility, noise, nonbeing,
   nonentity, nonexistence, nongratification, noninhabitance,
   nonoccupance, nonoccupancy, nonoccurrence, nonreality,
   nonresidence, nonsatisfaction, nonsensicality, nonsubsistence,
   not-being, nothingness, nugacity, nullity, opening, otiosity,
   outer space, painfulness, paleness, pallor, phatic communion,
   place open, pointlessness, pokiness, polydipsia, ponderousness,
   profitlessness, proportion, purposelessness, rat race, relish,
   savorlessness, senselessness, shallowness, silliness, slenderness,
   slightness, slowness, solemnity, sophistry, space,
   spatial extension, sphere, spiritlessness, spleen, spread,
   staleness, sterility, stiffness, stodginess, stomach, stuffiness,
   superficial extension, superficiality, surface, sweet tooth,
   tapeworm, taste, tastelessness, tediousness, tedium, the absurd,
   thirst, thirstiness, tongue in cheek, torment of Tantalus, tract,
   triflingness, triteness, triviality, trivialness, unactuality,
   uncandidness, uncandor, uncomfortableness, unease, uneasiness,
   unfrankness, unhappiness, uninterestingness, unliveliness,
   unmeaningness, unpleasure, unproductiveness, unprofitability,
   unprofitableness, unreality, unsatisfaction, unsignificancy,
   uselessness, vacancy, vacant post, vacantness, vacuity,
   vacuousness, vacuum, valuelessness, vanity, vapidity, vapidness,
   vexation of spirit, vicious circle, void, voidness, volume,
   woodenness, worthlessness