Boulder is a geological term used to describe a large, rounded ROCK or STONE. It is often found in rivers, streams, and other bodies of water. The term can also refer to a large mass of ROCK that has been moved by natural forces such as glaciers or erosion. The term 'ROCK' is a four-letter word for boulder, while 'STONE' is a five-letter word. A DAM is a three-letter word for a structure built to contain water, and 'DAMS' is a four-letter word for the plural form. The Rocky Mountains are a seven-letter word for a mountain range located in western North America.