Peter Mark Roget (1779-1869) is so identified with his famous thesaurus, still in print more than 150 years after his death, that it would not be surprising if one found his name as a synonym for thesaurus in a thesaurus. "Roget has become a generic term for any book that supplies synonyms and antonyms," one editor has said.
What was unique about Roget's thesaurus was not that it was a book of synonyms but that it was organized in an original way. He came up with nearly 1,000 concepts into which all the words in the English language could be divided. To find the right word, one first needed to determine the right concept. This proved a bit cumbersome for most people, so later editions retained the concepts - there are now 990 of them - but placed words in alphabetical order so synonyms would be easier to find.
One wonders if Roget would approve of the modern Roget's Thesaurus if he could inspect a copy. Would it satisfy or offend his own sense of order?