The term 'Plains Natives' refers to the indigenous people of the Great Plains region of North America. The four-letter answer OTOS is an abbreviation for the Otoe tribe, a Native American people who traditionally lived in Nebraska, Kansas, Iowa, and Oklahoma. The six-letter answer OMAHAS is an abbreviation for the Omaha tribe, a Native American people who traditionally lived in Nebraska and Iowa. The five-letter answer OTOES is an abbreviation for the Otoe-Missouria tribe, a Native American people who traditionally lived in Oklahoma.