rodent (n.) Look up rodent at Dictionary.com
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.)).