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a reference resource that contains groups of words that have similar meanings. A thesaurus may be published as a printed book, or as a digital product such as a website or app.

Origin and usage

Thesaurus entered English in the 16th century from Latin. It comes ultimately from the Greek word ‘thēsauros’, meaning a storehouse or treasury.


For the first three centuries of its use in English, the term thesaurus was used broadly to mean any work containing a store of knowledge, such as a dictionary or encyclopedia. It was not until 1852, when a British doctor and lexicographer called Peter Mark Roget published his Thesaurus of words divided according to categories rather than alphabetically, that the meaning narrowed. Roget’s declared aim was to help those ‘struggling with the difficulties of composition’ by offering alternative words for them to use. While Roget’s Thesaurus, which is still in print, maintains his original structure of classes and subdivisions based ultimately on the philosophy of Leibniz, other thesauruses – or should that be thesauri? – follow a different structure.

In the Macmillan Thesaurus, which is now available online as an independent, fully searchable resource, every word or phrase in every entry is linked to a meaning in the dictionary, which means that all the resources of both Macmillan Dictionary and the Macmillan Thesaurus are available together.


“I keep a hotel room in my town, although I have a large house … I work on yellow pads and with ballpoint pens. I keep a Bible, a thesaurus, a dictionary, and a bottle of sherry.”
(Maya Angelou)

Related words

almanac, compendium, dictionary, encyclopedia

View the full definition in the Macmillan Dictionary.

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