The Collaborative International Dictionary of English v.0.48:

Imperfection \Im`per*fec"tion\, n. [L. imperfectio: cf. F.
   imperfection. See Imperfect, a.]
   The quality or condition of being imperfect; lack of
   perfection; incompleteness; deficiency; fault or blemish.
   [1913 Webster]

         Sent to my account
         With all my imperfections on my head.    --Shak.

   Syn: Defect; deficiency; incompleteness; fault; failing;
        weakness; frailty; foible; blemish; vice.
        [1913 Webster]

WordNet (r) 3.0 (2006):

imperfection
    n 1: the state or an instance of being imperfect [syn:
         imperfection, imperfectness] [ant: flawlessness, ne
         plus ultra, perfection]