Source : Webster's Revised Unabridged Dictionary (1913)

Inefficiency \In`ef*fi"cien*cy\, n.
   The quality of being inefficient; want of power or energy
   sufficient; want of power or energy sufficient for the
   desired effect; inefficacy; incapacity; as, he was discharged
   from his position for inefficiency.

Source : WordNet®

inefficiency
     n : unskillfulness resulting from a lack of efficiency [ant: {efficiency}]