Roget described his thesaurus in the foreword to the first edition: It is now nearly fifty years since I first projected a system of verbal classification similar to that on which the present work is founded.
Conceiving that such a compilation might help to supply my own deficiencies, I had, in the year 1805, completed a classed catalogue of words on a small scale, but on the same principle, and nearly in the same form, as the Thesaurus now published.
This may be conceptualized as a tree containing over a thousand branches for individual "meaning clusters" or semantically linked words.
Although these words are not strictly synonyms, they can be viewed as colours or connotations of a meaning or as a spectrum of a concept.
[citation needed] One of the most general words is chosen to typify the spectrum as its headword, which labels the whole group.