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]