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For the American rapper, see TheSaurus (rapper).

A thesaurus is an indexed compilation of words with similar, related, and opposite meanings: for example, a book of jargon for a specialized field.

The first example of this genre, Roget's Thesaurus, was compiled in 1805 by Peter Roget, and published in 1852. Entries in Roget's Thesaurus are listed conceptually rather than alphabetically.

Although including synonyms and antonyms, entries in a thesaurus should not be taken as a list of them. The entries are also designed for drawing distinctions between similar words and assisting in choosing exactly the right word. Nor does a thesaurus entry define words. That work is left to the dictionary.

In information technology, a thesaurus represents a database or list of semantically orthogonal topical search keys. In the field of Artificial Intelligence, a thesaurus may sometimes be referred to as an ontology.

Thesaurus databases, created by international standards, are generally arranged hierarchically by themes and topics. Such a thesaurus places each term in context, allowing a user to distinguish between "bureau" the office and "bureau" the furniture. A thesaurus of this type is often used as the basis of an index for online material. The Art and Architecture Thesaurus, for example, is used to index the national databases of museums, Artefacts Canada, held by the Canadian Heritage Information Network (CHIN).

Contents 1 Etymology 2 Definition 3 Examples 3.1 Specialized 4 See also 5 References 6 External links

The word "thesaurus" is derived from 16th-century New Latin, in turn from Latin thesaurus, from ancient Greek θησαυρός thesauros, meaning "storehouse" or "treasury" (and thus (and thus the medieval rank of thesaurer was a synonym for treasurer). This meaning has been largely supplanted by Roget's usage of the term.

A formal definition of a thesaurus designed for indexing is:

• a list of every important term (single-word or multi-word) in a given domain of knowledge; and
• a set of related terms for each term in the list.

As such, it is a list of subject headings and cross-references used in the filing and retrieval of documents.

Terms are the basic semantic units for conveying concepts. They are usually single-word nouns, since nouns are the most concrete part of speech. Verbs can be converted to nouns -- "cleans" to "cleaning", "reads" to "reading", and so on. Adjectives and adverbs, however, seldom convey any meaning useful for indexing. When a term is ambiguous, a “scope note” can be added to ensure consistency, and give direction on how to interpret the term. Not every term needs a scope note, but their presence is of considerable help in using a thesaurus correctly and reaching a correct understanding of the given field of knowledge.

"Term relationships" are links between terms that often describe synonyms, near-synonyms, or hierarchical relations. Synonyms and near-synonyms are indicated by a "Related Term" (RT). The way the term "Cybernetics" is related to the term "Computers" is an example of such a relationship. Hierarchical relationships are used to indicate terms which are narrower and broader in scope. A "Broader Term" (BT) is a more general term, e.g. “Apparatus” is a generalization of “Computers”. Reciprocally, a Narrower Term (NT) is a more specific term, e.g. “Digital Computer” is a specialization of “Computer”. BT and NT are reciprocals; a broader term necessarily implies at least one other term which is narrower. Thesaurus designers are generally careful to ensure that BT and NT indicate class relationships, as distinguished from part-whole relationships. Some thesauri also include Use (USE) and Used For (UF) indicators when an authorized term is to be used for another, unauthorized, term; for example, the entry for the authorized term "Frequency" could have the indicator "UF Pitch". Reciprocally, the entry for the unauthorized term "Pitch" would have the indicator "USE Frequency". Used For (UF) terms are often called "entry points" into the thesaurus, "pointing" to the chosen term (the Preferred Term or Descriptor) that has been chosen to stand for the concept. As such, their presence in text can be use by automated indexing software to suggest the Preferred Term being used as an Indexing Term.

• Thesaurus of English Words & Phrases (ed. P. Roget); ISBN 0-06-272037-6, see: Roget's Thesaurus.
• The Synonym Finder (ed. J. I. Rodale); ISBN 0-87857-236-8
• Webster's New World Thesaurus (ed. C. Laird); ISBN 0-671-51983-2
• Oxford American Desk Thesaurus (ed. C. Lindberg); ISBN 0-19-512674-2
• Random House Word Menu by Stephen Glazier; ISBN 0-679-40030-3, a blend of thesaurus, dictionary, and glossary.

An important thesaurus project of recent years is the Historical Thesaurus of English (HTE), currently in progress at the University of Glasgow. The HTE, which started in 1964, will be a complete database of all the words in the second edition of the Oxford English Dictionary, arranged by semantic field and date. In this way, the HTE arranges the whole vocabulary of English from the earliest written records (in Anglo-Saxon) to the present alongside types and dates of use. As a historical thesaurus, it will be the first for any of the world's languages. The HTE project has already produced the Thesaurus of Old English^[1], which is derived from the whole HTE database.^[2].

• NAL Agricultural Thesaurus, (United States National Agricultural Library, United States Department of Agriculture)
• Evaluation Thesaurus (by. M. Scriven); ISBN 0-8039-4364-4
• Great Song Thesaurus (by R. Lax & F. Smith); ISBN 0-19-505408-3
• Thesaurus of Psychological Index Terms (APA); ISBN 1-55798-775-0
• Clinician's Thesaurus, (by E.Zuckerman); ISBN 1-57230-569-X
• Art and Architecture Thesaurus, (Getty Institute)
• AGROVOC Thesaurus, (Food and Agriculture Organization of the United Nations)
• GEneral Multilingual Environmental Thesaurus, (European Environment Agency)

• Controlled vocabulary
• Dictionary
• Ontology (computer science)
• Simple Knowledge Organisation System
• WordNet

• Roget's International Thesaurus
• TemaTres: open source thesaurus management
• Aiksaurus: open source and online thesaurus
• [1] One of the few examples of the old-style categorical listings available online.