Source : Webster's Revised Unabridged Dictionary (1913)

Deficient \De*fi"cient\, a. [L. deficiens, -entis, p. pr. of
   deficere to be wanting. See {Defect}.]
   Wanting, to make up completeness; wanting, as regards a
   requirement; not sufficient; inadequate; defective;
   imperfect; incomplete; lacking; as, deficient parts;
   deficient estate; deficient strength; deficient in judgment.

         The style was indeed deficient in ease and variety.
                                                  --Macaulay.

   {Deficient number}. (Arith.) See under {Abundant}. --
      {De*fi"cient-ly}, adv.

Source : WordNet®

deficient
     adj 1: inadequate in amount or degree; "a deficient education";
            "deficient in common sense"; "lacking in stamina";
            "tested and found wanting" [syn: {lacking(p)}, {wanting(p)}]
     2: of a quantity not able to fulfill a need or requirement;
        "insufficient funds" [syn: {insufficient}] [ant: {sufficient}]
     3: falling short of some prescribed norm; "substandard housing"
        [syn: {inferior}, {substandard}]