Not competent; wanting in adequate strength, power, capacity, means, qualifications, or the like; incapable; unable; inadequate; unfit.

Wanting the legal or constitutional qualifications; inadmissible; as, a person professedly wanting in religious belief is an incompetent witness in a court of law or equity; incompetent evidence; a mentally defective person is incompetent to care for himself and requires a legal guardian.

lacking the mental ability to understand the nature and effects of one’s decisions.

One who lacks ability, legal qualification, or fitness to manage his own affairs.

Not lying within one's competency, capacity, or authorized power; not permissible.

someone who is not competent to take effective action

See "Capacity."