The Collaborative International Dictionary of English v.0.48:

Perspicacity \Per`spi*cac"i*ty\
   (p[~e]r`sp[i^]*k[a^]s"[i^]*t[y^]), n. [L. perspicacitas: cf.
   F. perspicacit['e]. See Perspicacious.]
   The state of being perspicacious; acuteness of sight or of
   intelligence; acute discernment. --Sir T. Browne.
   [1913 Webster]

WordNet (r) 3.0 (2006):

perspicacity
    n 1: intelligence manifested by being astute (as in business
         dealings) [syn: shrewdness, astuteness, perspicacity,
         perspicaciousness]
    2: the capacity to assess situations or circumstances shrewdly
       and to draw sound conclusions [syn: judgment, judgement,
       sound judgment, sound judgement, perspicacity]