thesaurus

noun, plural the·sau·rus·es, the·sau·ri [-sawr-ahy] /-ˈsɔr aɪ/.

1. a dictionary of synonyms and antonyms, such as the online Thesaurus.com.
2. any dictionary, encyclopedia, or other comprehensive reference book.
3. a storehouse, repository, or treasury.
4. Computers.
   1. an index to information stored in a computer, consisting of a comprehensive list of subjects concerning which information may be retrieved by using the proper key terms.
   2. a dictionary of synonyms and antonyms stored in memory for use in word processing.

noun, plural online thesauruses, online thesauri.

1. a thesaurus or dictionary of words with the same or nearly the same meanings, or synonyms, and their opposites, or antonyms, such as Thesaurus.com, available on the Internet or the World Wide Web, accessed through a web browser, and used by entering a query term into a search box on the site. An online thesaurus provides immediate electronic access to lists of alternate terms for the queried word, covering its various shades of meaning: This online thesaurus showed me that smart, as an adjective, not only means intelligent, but also stylish, or lively, and gave long lists of other words for each meaning.

noun plural -ruses or -ri (-raɪ)

1. a book containing systematized lists of synonyms and related words
2. a dictionary of selected words or topics
3. rare a treasury

n.1823, “treasury, storehouse,” from Latin thesaurus “treasury, treasure,” from Greek thesauros “a treasure, treasury, storehouse, chest,” from root of tithenai “to put, to place.” The meaning “encyclopedia filled with information” is from 1840, but existed earlier as thesaurarie (1590s), used as a title by early dictionary compilers. Meaning “collection of words arranged according to sense” is first attested 1852 in Roget’s title. Thesaur is attested in Middle English with the meaning “treasure” (15c.-16c.).