beaver

1 :  a piece of armor protecting the lower part of the face

2 :  a helmet visor

:  to work energetically beavering away at the problem

1 river 280 miles (451 kilometers) long in northwestern Oklahoma forming the upper course of the North Canadian River

2 river 305 miles (491 kilometers) long Canada in Alberta and Saskatchewan flowing east into the Churchill River

:  an animal that has thick brown fur, webbed hind feet, and a broad flat tail, that cuts down trees with its teeth, and that builds dams and houses of sticks and mud in water