sigmodont

from The Century Dictionary.

• Showing a sigmoid pattern of the molar crowns when the biserial tubercles of these teeth are ground flat by wear, as a murine; of or pertaining to the Sigmodontes, as any murine indigenous to America.
• noun Any sigmodont murine.

from the GNU version of the Collaborative International Dictionary of English.

• noun (Zoöl.) Any one of a tribe (Sigmodontes) of rodents which includes all the indigenous rats and mice of America. So called from the form of the ridges of enamel on the crowns of the worn molars. Also used adjectively.

from Wiktionary, Creative Commons Attribution/Share-Alike License.

• noun zoology Any of the Sigmodontes tribe of rodents, including all the indigenous rats and mice of America.