Mo. Rev. Stat. § 474.395: No-contest clauses, application of, petition may be filed — definition.

1. If a will contains a no-contest clause, an interested person may file a petition with the court for a determination whether a particular motion, petition, action, or other claim for relief by the interested person would trigger application of the no-contest clause or would otherwise trigger a forfeiture that is enforceable under applicable law and public policy, which application would be adjudicated in the manner prescribed in section 456.4-420, and subject to the provisions set forth therein.

2. For purposes of this section, a "no-contest clause" shall mean a provision in a will purporting to rescind a donative transfer to, or a fiduciary appointment of, any person who institutes a proceeding challenging the validity of all or part of the will, or that otherwise effects a forfeiture of some or all of an interested person's beneficial interest in the estate as a result of some action taken by the beneficiary. This definition shall not be construed in any way as determining whether a no-contest clause is enforceable under applicable law and public policy in a particular factual situation. As used in this section, the term "no-contest clause" shall also mean an "in terrorem clause".