A reference source provides answers to brief facts, statistical information, and background information, or directs you to the additional information sources. The reference sources are standard works that are used to locate the specific types of information.Although the term reference book is frequently used, reference sources may be books, serials, online databases, or the internet.Reference sources include dictionaries, thesaurus, encyclopedias, handbooks, yearbooks, almanacs, directories, and biographical and geographical sources.Thesaurus:In this reference book, words that have the same or similar meaning (synonyms and sometimes antonyms) are grouped together.In contrast to a dictionary, which helps to find the meaning and pronunciation of the words, a thesaurus helps to find the most appropriate word to express an idea and also other related words.Example of Thesaurus: The Merriam-Websters Thesaurus Hint Dictionary: A dictionary is a book containing words of a language arranged alphabetically with their meanings. Most dictionaries tell us much more than the meaning of the words.An anthology is a book that contains pieces of writing or poems, often on the same subject, by different authors.Pronunciation Guide: For the reader's convenience Pronunciation Guide lists the entire range of difficult-to-pronounce-correctly words at the back or front of the book.Thus, we can conclude that we need a Thesaurus to find only the synonyms and antonyms of the words.