scienceblog.com
Peter Mark Roget began privately arranging words by meaning in 1805, while still a young physician. After leaving medical practice at 61, he spent twelve years turning that lifelong habit into a classification of the English language; he published it at 73, and Roget’s Thesaurus has never gone out of print in more than 170 years.
Roget's famous reference work grew from a private catalogue begun in 1805. Its long development, idea-first structure and continuing revisions make the real story richer than a simple retirement tale.