Thesaurus

In general usage, a thesaurus is a reference work that lists words grouped together according to similarity of meaning (containing synonyms and sometimes antonyms), in contrast to a dictionary, which provides definitions for words, and generally lists them in alphabetical order. The main purpose of such reference works is to help the user "to find the word, or words, by which [an] idea may be most fitly and aptly expressed" – to quote Peter Mark Roget, architect of the best known thesaurus in the English language.

Although including synonyms, a thesaurus should not be taken as a complete list of all the synonyms for a particular word. The entries are also designed for drawing distinctions between similar words and assisting in choosing exactly the right word. Unlike a dictionary, a thesaurus entry does not give the definition of words.

In library science and information science, thesauri have been widely used to specify domain models. Recently, thesauri have been implemented with Simple Knowledge Organization System (SKOS).

The word "thesaurus" is derived from 16th-century New Latin, in turn from Latin , which is the Latinisation of the Greek (thēsauros), "treasure, treasury, storehouse". The word thēsauros is of uncertain etymology. Douglas Harper derives it from the root of the Greek verb τιθέναι tithenai, "to put, to place."Robert Beekes rejected an Indo-European derivation and suggested a Pre-Greek suffix *-ar^wo-.

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