A word book is a collection of words and their definitions. The three most common types of word books are lexicons, thesauruses, and dictionaries. A LEXICON is a book containing an alphabetical arrangement of the words in a language and their definitions. A THESAURUS is a book of synonyms and antonyms, which are words that have similar or opposite meanings. A DICTIONARY is a book that contains an alphabetical list of words, with information given for each word, usually including definition, pronunciation, and etymology.