incompetent

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

• adjective Lacking qualities necessary for effective conduct or action.
• adjective Inadequate for or unsuited to a particular purpose or application.
• adjective Not functioning properly in the body.
• adjective Not legally qualified, as testimony that does not meet the standards for admissibility or a juror whose personal interest in the outcome of the case does not allow him or her to serve.
• adjective Lacking sufficient mental ability or awareness.
• noun An incompetent person.

from The Century Dictionary.

• noun An incompetent person; one who is mentally or physically deficient.
• Not competent; wanting ability or qualification; unable; incapable; inadequate.
• In law, not competent; not qualified; incapacitated.
• Synonyms Insufficient, unfit, disqualified.

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

• adjective Not competent; wanting in adequate strength, power, capacity, means, qualifications, or the like; incapable; unable; inadequate; unfit.
• adjective (Law) Wanting the legal or constitutional qualifications; inadmissible
• adjective Not lying within one's competency, capacity, or authorized power; not permissible.

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

• adjective Unskilled, lacking normally expected degree of ability, Northern Victorian Irrigation Renewal Project like see ombudsmans report.
• adjective Unable to make rational decisions, insane or otherwise cognitively impaired.
• noun A person who is incompetent.

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

• adjective not qualified or suited for a purpose
• adjective not doing a good job
• adjective legally not qualified or sufficient
• noun someone who is not competent to take effective action
• adjective showing lack of skill or aptitude
• adjective not meeting requirements