Synonyms of words are found in a thesaurus, which is a reference book set up like a dictionary. Words are listed in alphabetical order along with a list of synonyms and antonyms that can be used in its place. The online thesaurus is located at Thesaurus.com.
Its main purpose is to help the user find a better or more appropriate word to describe something. The concept of the thesaurus has been around since as early as the 4th century, but Peter Mark Roget published the first modern thesaurus in 1852. It was called "Roget's Thesaurus." Since then, many versions have been published and it has never been out of print.