The Collaborative International Dictionary of English v.0.48:

Nothingness \Noth"ing*ness\, n.
   1. Nihility; nonexistence.
      [1913 Webster]

   2. The state of being of no value; a thing of no value.
      [1913 Webster]

WordNet (r) 3.0 (2006):

nothingness
    n 1: the state of nonexistence [syn: nothingness, void,
         nullity, nihility]
    2: empty rhetoric or insincere or exaggerated talk; "that's a
       lot of wind"; "don't give me any of that jazz" [syn: wind,
       malarkey, malarky, idle words, jazz, nothingness]

Moby Thesaurus II by Grady Ward, 1.0:

75 Moby Thesaurus words for "nothingness":
   KO, absence, acreage, area, blackout, blank, breadth, catalepsy,
   catatonia, catatony, clean slate, coma, continuum, deprivation,
   dimension, emptiness, empty space, expanse, expansion, extension,
   extent, faint, field, galactic space, grayout, inanity,
   infinite space, interstellar space, kayo, knockout, lipothymia,
   lipothymy, measure, nada, negation, negativeness, negativity,
   nihility, nirvana, nirvana principle, nonbeing, nonentity,
   nonexistence, nonoccurrence, nonreality, nonsubsistence, not-being,
   nothing, nullity, oblivion, obliviousness, outer space, proportion,
   semiconsciousness, senselessness, sleep, space, spatial extension,
   sphere, spread, stupor, superficial extension, surface, swoon,
   syncope, tabula rasa, tract, unactuality, unconsciousness,
   unreality, vacancy, vacuity, vacuum, void, volume