The Collaborative International Dictionary of English v.0.48:

Deficiency \De*fi"cien*cy\, n.; pl. Deficiencies. [See
   Deficient.]
   The state of being deficient; inadequacy; want; failure;
   imperfection; shortcoming; defect. "A deficiency of blood."
   --Arbuthnot.
   [1913 Webster]

         [Marlborough] was so miserably ignorant, that his
         deficiencies made him the ridicule of his
         contemporaries.                          --Buckle.
   [1913 Webster]

   Deficiency of a curve (Geom.), the amount by which the
      number of double points on a curve is short of the maximum
      for curves of the same degree.
      [1913 Webster]