The term 'Large Amphibious Rodent' refers to the BEAVER, a 6-letter word. The BEAVER is a large rodent that is native to North America and Eurasia. It is an aquatic mammal that is well-known for its ability to build dams and lodges in rivers and streams. Its diet consists of bark, cambium, roots, and aquatic plants. The BEAVER is an important species in many ecosystems, as it helps to create wetlands and provide habitat for other animals.