The Collaborative International Dictionary of English v.0.48:

Pellucidity \Pel`lu*cid"i*ty\, Pellucidness \Pel*lu"cid*ness\,
   n. [L. pelluciditas.]
   The quality or state of being pellucid; transparency;
   translucency; clearness; as, the pellucidity of the air.
   --Locke.
   [1913 Webster]

WordNet (r) 3.0 (2006):

pellucidity
    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]