The Collaborative International Dictionary of English v.0.48:

Lucidity \Lu*cid"i*ty\, n. [Cf. F. lucidit['e]. See Lucid.]
   The quality or state of being lucid.
   [1913 Webster]

WordNet (r) 3.0 (2006):

lucidity
    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: a lucid state of mind; not confused