fixity

from WordNet (r) 3.0 (2006)

fixity
    n 1: the quality of being fixed in place as by some firm
         attachment [syn: {fastness}, {fixedness}, {fixity},
         {fixture}, {secureness}] [ant: {looseness}]
    2: the quality of being incapable of mutation; "Darwin
       challenged the fixity of species" [syn: {immutability},
       {immutableness}, {fixity}] [ant: {mutability}, {mutableness}]

from The Collaborative International Dictionary of English v.0.48

Fixity \Fix"i*ty\ (-[i^]*t[y^]), n. [Cf. F. fixit['e].]
   1. Fixedness; as, fixity of tenure; also, that which is
      fixed.
      [1913 Webster]

   2. Coherence of parts. --Sir I. Newton.
      [1913 Webster]