rodent (n.)
1835 (as an adjective 1833), from Modern Latin Rodentia, the order name, from Latin rodentem (nominative rodens), present participle of rodere "to gnaw, eat away," from PIE root *red- "to scrape, scratch, gnaw" (cognates: Sanskrit radati "scrapes, gnaws," radanah "tooth;" Latin radere "to scrape;" Welsh rhathu "scrape, polish"). Uncertain connection to Old English rætt (see rat (n.)).