The Historical Thesaurus of the Oxford English Dictionary (HTOED) is the largest thesaurus in the world, conceived and compiled by the English Language Department of the University of Glasgow.

The word "thesaurus" is derived from 16th-century New Latin, in turn from Latin thesaurus, from ancient Greek θησαυρός thesauros, meaning a collection of things which are of big importance or value (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.

The Historical Thesaurus of the Oxford English Dictionary (HTOED) is the largest thesaurus in the world, conceived and compiled by the English Language Department of the University of Glasgow. The HTOED is 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 HTOED arranges the whole vocabulary of English, from the earliest written records in Old English to the present, alongside types and dates of use. It is the first historical thesaurus to be compiled for any of the world's languages and contains 800,000 meanings for 600,000 words, within 230,000 categories, covering more than 920,000 words and meanings, and making it double the size of Roget’s version.

Oxford University Press announced in June 2010 that the contents of the Historical Thesaurus would be incorporated into the OED Online when it is relaunched in December.

tags: Thesaurus.