Roget's Thesaurus is First Published 50 Years After its Composition

On April 29, 1852 British physician, natural theologian and lexicographer Peter Mark Roget  published his Thesaurus of English Words and Phrases Classified so as to Facilitate the Expression of Ideas and to Assist in Literary Composition, the manuscript for which he had originally written in 1805, nearly 50 years before publication. The 15,000 words it contained were arranged conceptually rather than alphabetically, incorporating 1002 concepts, in six classes derived from Aristotelian, Leibnizian principles of classification:

1. Abstraction Relations
2. Space
3. Matter
4. Intellect
5. Volition
6. Affections

The Thesaurus contained synonyms, in contrast to a dictionary, which contains definitions and pronunciations. 

"Roget's Thesaurus is composed of six primary classes. Each class is composed of multiple divisions and then sections. This may be conceptualized as a tree containing over a thousand branches for individual "meaning clusters" or semantically linked words. These words are not exactly synonyms, but can be viewed as colours or connotations of a meaning or as a spectrum of a concept. One of the most general words is chosen to typify the spectrum as its headword, which labels the whole group. 

"Roget's schema of classes and their subdivisions is based on the philosophical work of Leibniz (see Leibniz — Symbolic thought), itself following a long tradition of epistemological work starting with Aristotle. Some of Aristotle's Categories are included in Roget's first class "abstract relations". The Wikipedia "category schemes" are also based on the same principles" (Wikipedia article on Roget's Thesaurus, accessed 11-28-2008).

"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.

"Thesaurus databases, created by international standards, are generally arranged hierarchically by themes and topics. Such a thesaurus places each term in context, allowing a user 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. The Art and Architecture Thesaurus, for example, is used to index the national databases of museums" (Wikipedia article on Thesaurus, accessed 11-28-2008).

The printing of the first edition was 1000 copies. The original manuscript for Roget's Thesaurus is preserved in the Karpeles Manuscript Library Museum. 

Kendall, The Man Who Made Lists: Love, Death, Madness, and the Creation of Roget's Thesaurus (2008).