Source : Webster's Revised Unabridged Dictionary (1913)

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

Source : WordNet®

insubstantiality
     n 1: lack of solid substance and strength
     2: lacking substance or reality [ant: {substantiality}]