This name is an abbreviation for
"Rosh Metivta" (Head of the Yeshiva). Probably a family whose Head held that position would use this as their name. It is an old Jewish custom to use abbreviations from the initials or syllables of other names or words. It
was common to refer to famous Rabbis and Sages such as Rashi and Rambam by abbreviations based on their Hebrew titles and names.