The Collaborative International Dictionary of English v.0.48:

Perspicuity \Per`spi*cu"i*ty\ (p[~e]r`sp[i^]*k[=u]"[i^]*t[y^]),
   n. [L. perspicuitas: cf. F. perspicuit['e].]
   1. The quality or state of being transparent or translucent.
      [Obs.] --Sir T. Browne.
      [1913 Webster]

   2. The quality of being perspicuous to the understanding;
      clearness of expression or thought.
      [1913 Webster]

   3. Sagacity; perspicacity.
      [1913 Webster]

   Syn: Clearness; perspicuousness; plainness; distinctness;
        lucidity; transparency. See Clearness.
        [1913 Webster]

WordNet (r) 3.0 (2006):

perspicuity
    n 1: clarity as a consequence of being perspicuous [syn:
         perspicuity, perspicuousness, plainness]