incompetent

Lacking qualities necessary for effective conduct or action.

Inadequate for or unsuited to a particular purpose or application.

Not functioning properly in the body.

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.

Lacking sufficient mental ability or awareness.

An incompetent person.

An incompetent person; one who is mentally or physically deficient.

Not competent; wanting ability or qualification; unable; incapable; inadequate.