The Collaborative International Dictionary of English v.0.48:

Insubstantiality \In`sub*stan`ti*al"i*ty\, n.
   Unsubstantiality; unreality. [R.]
   [1913 Webster]

WordNet (r) 3.0 (2006):

insubstantiality
    n 1: lack of solid substance and strength
    2: lacking substance or reality [ant: solidness,
       substantiality, substantialness]

Moby Thesaurus II by Grady Ward, 1.0:

77 Moby Thesaurus words for "insubstantiality":
   airiness, airy nothing, airy texture, attenuation, bodilessness,
   danger, delicacy, desultoriness, diaphanousness, dilutedness,
   dilution, ethereality, exiguity, exility, fineness, flimsiness,
   frailty, gauziness, gossameriness, gracility, hazard,
   immateriality, impalpability, imponderability, incorporeality,
   infirmity, insecurity, insolidity, instability, intangibility,
   laciness, lightness, mistiness, paperiness, peril, perilousness,
   precariousness, rareness, rarity, risk, riskiness, shakiness,
   shiftiness, shiftingness, slenderness, slightness, slimness,
   slipperiness, speculativeness, subtility, subtilty, subtlety,
   tenuity, tenuousness, thinness, ticklishness, treacherousness,
   treachery, unauthenticity, unauthoritativeness, unconcreteness,
   undependability, unfaithworthiness, unreality, unreliability,
   unsolidity, unsoundness, unsteadfastness, unsteadiness,
   unsubstantiality, unsubstantialness, unsureness, untrustworthiness,
   vagueness, wateriness, weakness, wispiness