A thesaurus, from the Greek for "storehouse" or "treasure," is a catalog of words and phrases designed to facilitate literary composition. Like a dictionary of synonyms, it groups related words together, but unlike such a dictionary it is arranged conceptually, with entries organized without regard to spelling. These headings are further divided according to meaning and parts of speech, so that the word biased, for example, might be found under the category "obliquity" (grouped with the related adjectives leaning, beveled, and sloped) and also under "narrow-mindedness" (along with prejudiced, one-sided, and partial). An alphabetical index lists entries.
The British cleric John Wilkins brought out a "conceptual dictionary," with tables, as early as 1668. The first successful example, however, was devised by Peter Mark Roget (1779-1869), a British physician who produced his Thesaurus of English Words and Phrases in 1852. The work was immediately popular and had gone through 28 editions by Roget's death. Subsequent revised editions were overseen first by his son and grandson and, after 1886, by the New York firm of Thomas Y. Crowell, which has published the work ever since. Roget's International Thesaurus remains the standard by which other thesauri--including those of Francis March (1902) and Norman Lewis (1958)--are judged.