THE THESAURUS A thesaurus is a collection of words with similar meanings, usually presented in alphabetical order. These words are called synonyms. A thesaurus is useful when you want to change a word to another word with a similar meaning. The entries in a thesaurus typically contain the synonyms in most frequent to least frequent occurrence. In a modern thesaurus, guide words also appear at the tops of pages. They function the same way as guide words in dictionaries, indicating the first and l