The Collaborative International Dictionary of English v.0.48:

Defective \De*fect"ive\, n.
   1. Anything that is defective or lacking in some respect.
      [Webster 1913 Suppl.]

   2. (Med.) One who is lacking physically or mentally.

   Note: Under the term defectives are included deaf-mutes, the
         blind, the feeble-minded, the insane, and sometimes,
         esp. in criminology, criminals and paupers.
         [Webster 1913 Suppl.]

The Collaborative International Dictionary of English v.0.48:

Defective \De*fect"ive\, a. [L. defectivus: cf. F. d['e]fectif.
   See Defect.]
   1. Wanting in something; incomplete; lacking a part;
      deficient; imperfect; faulty; -- applied either to natural
      or moral qualities; as, a defective limb; defective
      timber; a defective copy or account; a defective
      character; defective rules.
      [1913 Webster]

   2. (Gram.) Lacking some of the usual forms of declension or
      conjugation; as, a defective noun or verb. --
      De*fect"ive*ly, adv. -- De*fect"ive*ness, n.
      [1913 Webster]

WordNet (r) 3.0 (2006):

defective
    adj 1: having a defect; "I returned the appliance because it was
           defective" [syn: defective, faulty]
    2: markedly subnormal in structure or function or intelligence
       or behavior; "defective speech"
    3: not working properly; "a bad telephone connection"; "a
       defective appliance" [syn: bad, defective]

Moby Thesaurus II by Grady Ward, 1.0:

172 Moby Thesaurus words for "defective":
   aberrant, abroad, adrift, adulterated, all abroad, all off,
   all wrong, ament, amiss, amputee, arrested, askew, astray,
   at fault, awry, backward, beside the mark, blemished, born fool,
   broken, callow, checked, cicatrized, clot, congenital idiot,
   corrupt, corrupted, cracked, crazed, cretin, cripple, damaged,
   debased, deceptive, defaced, deficient, deformed, deformity,
   delusive, deranged, deviant, deviational, deviative, disfigured,
   disordered, distorted, disturbed, embryonic, errant, erring,
   erroneous, exceptional, failing, fallacious, fallible, false,
   faultful, faulty, flawed, found wanting, golem, half-assed,
   half-wit, handicapped person, heretical, heterodox, hypoplastic,
   idiot, illogical, illusory, imbecile, immature, impaired,
   imperfect, imprecise, impure, in arrear, in arrears, in default,
   in short supply, inaccurate, inadequate, incapable, incompetent,
   incomplete, inexact, infant, injured, insufficient, juggins,
   keloidal, kinked, lacking, makeshift, marred, mediocre,
   mentally deficient, missing, mixed, mongoloid idiot, moron,
   natural, natural idiot, natural-born fool, needing, not enough,
   not perfect, not right, not true, off, off the track, on the blink,
   on the fritz, out, out of order, paralytic, paraplegic, part,
   partial, patchy, peccant, perverse, perverted, pimpled, pimply,
   quadriplegic, retarded, scabbed, scabby, scant, scanty, scarified,
   scarred, scrappy, self-contradictory, short, shy, sick, simp,
   simple, simpleton, sketchy, split, straying, subnormal,
   the crippled, the handicapped, too little, twisted, underdeveloped,
   undeveloped, unequal to, uneven, unfactual, unfinished, unhealthy,
   unorthodox, unperfected, unproved, unqualified, unsatisfactory,
   unsatisfying, unsettled, unsound, unsufficing, unthorough, untrue,
   vitiated, wanting, warped, wide, wrong