From New World Encyclopedia
Peter Mark Roget, author of the first thesaurus.

A thesaurus is a dictionary type book of words that are organized by concepts and categories. It includes synonyms, related words, and/or antonyms. While dictionaries give definitions and pronunciations, thesauri usually do not. A thesaurus presents conceptually similar, broader, narrower, related, and contrasted terms. There are two types of thesauri: one for general use and another for the use in specific area such as medicine, arts, music, and others.

In information science, a thesaurus is a collection of controlled vocabularies which are used for indexing information. Thesaurus databases are generally arranged hierarchically by themes and topics. Such a thesaurus places each term in context, allowing a user, for example, 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.

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.


Did you know?
The word "thesaurus" comes from a Greek word meaning "treasury"

The word "thesaurus" is derived from sixteenth-century New Latin, in turn from Latin thesaurus, from ancient Greek θησαυρός thesauros, meaning "storehouse" or "treasury" (and thus the medieval rank of thesaurer was a synonym for treasurer).[1]


A formal definition of a thesaurus designed for indexing and information retrieval 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.

The National Information Standards Organization defines a thesaurus as:

A controlled vocabulary arranged in a known order and structured so that the various relationships among terms are displayed clearly and identified by standardized relationship indicators. Relationship indicators should be employed reciprocally.[2]

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

"Term relationships" are links between terms. These relationships can be divided into three types: hierarchical, equivalency or associative.


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. BT and NT are used to indicate class relationships, as well as part-whole relationships.


The equivalency relationship is used primarily to connect synonyms and near-synonyms. Use (USE) and Used For (UF) indicators are used 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," "lead-in terms," or "non-preferred terms," pointing to the authorized term (also referred to as 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.


Associative relationships are used to connect two related terms whose relationship is neither hierarchical nor equivalent. This relationship is described by the indicator "Related Term" (RT). The way the term "Cybernetics" is related to the term "Computers" is an example of such a relationship. Associative relationships should be applied with caution, since excessive use of RTs will reduce specificity in searches. Consider the following: if the typical user is searching with term "A," would they also want resources tagged with term "B"? If the answer is no, then an associative relationship should not be established.

Types of Thesaurus

There are two types of thesauri: general and special.


A number of general thesauri are available, including:

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,[3] which is derived from the whole HTE database.[4]


A specialized thesaurus is designed for particular user groups; discipline specific vocabularies and professional terms are selected and arranged. A number of thesauri are available including:

  • 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)

Online and electronic thesaurus

Online thesaurus

The online thesaurus is becoming popular due to the search behavioral changes of users. Advantages of an online thesaurus over print thesaurus are: search capability from multiple reference sources including etymological dictionary, dictionary, thesaurus, encyclopedia, web source index, and others; efficient and fast retrieval with a finger tip; cut-and-past capability of findings.

Online reference sources are often free for users since they are financially supported by advertisement income.

Electronic dictionary

An electronic dictionary is a compact electronic device, operated by a battery. Users can carry with them and use it without going online. The electronic dictionary usually includes a thesaurus as well as a number of references such as medical help book, foreign language phrase handbook, and others. The small devise often include from five to ten reference books.


The ANSI/NISO Z39.19 Standard of 2005 defines guidelines and conventions for the format, construction, testing, maintenance, and management of monolingual controlled vocabularies including lists, synonym rings, taxonomies, and thesauri.[5]

For multilingual vocabularies, the ISO 5964 Guidelines for the establishment and development of multilingual thesauri can be applied.

See also


ISBN links support NWE through referral fees

Books and journals

  • Broughton, Vanda. Essential Thesaurus Construction. London: Facet, 2006. ISBN 185604565X ISBN 9781856045650
  • Knapp, Sara D.The Contemporary Thesaurus of Search Terms and Synonyms: A Guide for Natural Language Computer Searching. Phoenix, AZ: Oryx Press, 2000.
  • Meltzer, Peter E. The Thinker's Thesaurus: Sophisticated Alternatives to Common Words. Oak Park, Ill: Marion Street Press, 2005.
  • Roget's II: The New Thesaurus. Boston: Houghton Mifflin, 1988. ISBN 0395483174 ISBN 9780395483176

Online sources

External links

All links retrieved April 30, 2023.


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