The Collaborative International Dictionary of English v.0.48:

Habitable \Hab"it*a*ble\ (h[a^]b"[i^]t*[.a]*b'l), a. [F.
   habitable, L. habitabilis.]
   Capable of being inhabited; that may be inhabited or dwelt
   in; as, the habitable world. -- Hab"it*a*ble*ness, n. --
   Hab"it*a*bly, adv.
   [1913 Webster]

WordNet (r) 3.0 (2006):

habitableness
    n 1: suitability for living in or on [syn: habitability,
         habitableness]