The Collaborative International Dictionary of English v.0.48:

Fluidity \Flu*id"i*ty\, n. [Cf. F. fluidit['e].]
   The quality of being fluid or capable of flowing; a liquid,
   a["e]riform, or gaseous state; -- opposed to solidity.
   [1913 Webster]

         It was this want of organization, this looseness and
         fluidity of the new movement, that made it penetrate
         through every class of society.          --J. R. Green.
   [1913 Webster]

WordNet (r) 3.0 (2006):

fluidity
    n 1: the property of flowing easily; "adding lead makes the
         alloy easier to cast because the melting point is reduced
         and the fluidity is increased"; "they believe that fluidity
         increases as the water gets warmer" [syn: fluidity,
         fluidness, liquidity, liquidness, runniness]
    2: a changeable quality; "a charming Oriental fluidity of
       manner"; "a certain fluidness in his perception of time made
       him an unpredictable colleague"; "demographers try to predict
       social fluidity" [syn: fluidity, fluidness]

Moby Thesaurus II by Grady Ward, 1.0:

54 Moby Thesaurus words for "fluidity":
   adaptability, adjustability, aeriness, alterability, changeability,
   changeableness, changefulness, chylifaction, chylification,
   ethereality, flatulence, flatuosity, flexibility, flow, fluency,
   fluidness, flux, fluxility, fluxion, gaseity, gaseous state,
   gaseousness, gassiness, impermanence, juiciness, lactation,
   lactescence, liquefaction, liquidness, malleability, milkiness,
   mobility, modifiability, moisture, movability, mutability,
   nonuniformity, permutability, plasticity, resilience, rheuminess,
   rubberiness, sappiness, serosity, succulence, suppleness,
   suppuration, transience, transitoriness, vapor pressure,
   vaporiness, vaporousness, wateriness, windiness