The term 'Burrowing South American Rodent' refers to the NUTRIA, a 6-letter word. NUTRIA are large, semi-aquatic rodents native to South America. They are known for their burrowing habits and have been introduced to other parts of the world, where they have become an invasive species. NUTRIA have thick, dark brown fur and webbed feet, and can grow up to 2 feet in length. They feed on aquatic plants and can cause significant damage to wetlands and other ecosystems.