Mo. Rev. Stat. § 544.010

The term "magistrate", as used in this chapter, shall mean those officers authorized by section 542.020 to issue process to preserve the peace, unless from the context of the law it appears that the term refers to magistrates created by Section 18 of Article V of the Constitution in effect on and prior to January 1, 1979, in which event the term shall mean an associate circuit judge or a division of the circuit court presided over by an associate circuit judge.