invariability

from WordNet (r) 3.0 (2006)

invariability
    n 1: a quality of uniformity and lack of variation [syn:
         {evenness}, {invariability}] [ant: {unevenness},
         {variability}]
    2: the quality of being resistant to variation [syn:
       {invariability}, {invariableness}, {invariance}] [ant:
       {variability}, {variableness}, {variance}]

from The Collaborative International Dictionary of English v.0.48

Invariability \In*va`ri*a*bil"i*ty\, n. [Cf. F.
   invariabilit['e].]
   The quality of being invariable; invariableness; constancy;
   uniformity.
   [1913 Webster]