The Collaborative International Dictionary of English v.0.48:

Limpidity \Lim*pid"i*ty\ (l[i^]m*p[i^]d"[i^]*t[y^]), n. [L.
   limpiditas: cf. F. limpidit['e].]
   The quality or state of being limpid.
   [1913 Webster]

WordNet (r) 3.0 (2006):

limpidity
    n 1: free from obscurity and easy to understand; the
         comprehensibility of clear expression [syn: clarity,
         lucidity, lucidness, pellucidity, clearness,
         limpidity] [ant: abstruseness, obscureness,
         obscurity, reconditeness, unclearness]
    2: passing light without diffusion or distortion [syn:
       pellucidness, pellucidity, limpidity]