The Collaborative International Dictionary of English v.0.48:

Inefficient \In`ef*fi"cient\, a.
   1. Not efficient; not producing the effect intended or
      desired, or achieiving the effect by unnnecessary and
      excessive expenditure of resources; inefficacious; as,
      inefficient means or measures; inefficient methods are too
      expensive.
      [1913 Webster +PJC]

   2. Incapable of, or indisposed to, effective action;
      habitually slack or remiss; effecting little or nothing;
      as, inefficient workmen; an inefficient administrator.
      [1913 Webster]

WordNet (r) 3.0 (2006):

inefficient
    adj 1: not producing desired results; wasteful; "an inefficient
           campaign against drugs"; "outdated and inefficient design
           and methods" [ant: efficient]
    2: lacking the ability or skill to perform effectively;
       inadequate; "an ineffective administration"; "inefficient
       workers" [syn: ineffective, inefficient]

Moby Thesaurus II by Grady Ward, 1.0:

42 Moby Thesaurus words for "inefficient":
   artless, careless, half-assed, inadept, inapt, inattentive,
   incapable, incapable of, incompetent, ineffective, ineffectual,
   inefficacious, inept, inexpert, inferior, mediocre, pedestrian,
   poor, skill-less, slipshod, slovenly, thoughtless, unable,
   unable to, unapt, undeft, undexterous, undextrous, unendowed,
   unfacile, unfit, unfitted, ungifted, unintelligent, unprepared,
   unproficient, unqualified, unskilled, unskillful, untalented,
   untrained, unworkmanlike