defective

from The American Heritage® Dictionary of the English Language, 5th Edition.

• adjective Having a defect; faulty.
• adjective Marked by subnormal structure, function, intelligence, or behavior.
• adjective Grammar Lacking one or more of the inflected forms normal for a particular category of word, as the verb may in English.
• noun One who has a physical or mental disability.

from The Century Dictionary.

• Having defect or flaw of any kind; imperfect; incomplete; lacking; faulty.
• Specifically In grammar, wanting some of the usual forms of declension or conjugation: as, a defective noun or verb.
• noun A person who is characterized by some special mental, moral, or physical defect; specifically, one who is deficient in one or more of the physical senses or powers.

from the GNU version of the Collaborative International Dictionary of English.

• noun Anything that is defective or lacking in some respect.
• noun (Med.) One who is lacking physically or mentally.
• adjective Wanting in something; incomplete; lacking a part; deficient; imperfect; faulty; -- applied either to natural or moral qualities
• adjective (Gram.) Lacking some of the usual forms of declension or conjugation.

from Wiktionary, Creative Commons Attribution/Share-Alike License.

• adjective Having one or more defects.
• adjective grammar, of a verb lacking some forms; e.g., having only one tense or being usable only in the third person.
• noun A person considered to be defective.

from WordNet 3.0 Copyright 2006 by Princeton University. All rights reserved.

• adjective markedly subnormal in structure or function or intelligence or behavior
• adjective having a defect
• adjective not working properly