Historical Thesaurus doesn't strike to the heart of what words mean
It's a dictionary of senses rather than of words. If you know what you mean, it will find the word that eluded you. For example, I have the sense 'country dweller' and I want a collective noun. HTOED allows me to find 'the ruralty'. It's a different way of thinking and is very cumbersome with the book, but the computerized version makes it reasonably easy.