Compound words are two or more words joined together in order to create a deeper meaning. They can be used as different parts of speech in a sentence and function in different ways depending on the meaning conveyed. Compound words are generally classified by their form: open, closed, and hyphenated. Open compounds are two separate words that create a new meaning, like hot dog or cell phone. Closed compounds occur when two words join to create one word with a new meaning, like bookstore or doghouse. Hyphenated compounds are two words joined with a hyphen, usually an adjective, like open-minded or sister-in-law.