There are many good sources both to find synonyms for a word, and to understand what is the difference between the words.
- Ludwig Ramshorn has written Dictionary of Latin Synonymes: For the Use of Schools and Private Students, which is now in the public domain. This is extensive dictionary that illustrate the difference between the words.
- Jean Baptiste Gardin Dumesnil’s Latin Synonyms: With Their Different Significations, close in style to Ramshorn’s book (and also in the public domain).
- Döderlein’s Hand-book of Latin Synonymes by Ludwig von Doederlein was transcibed by Project Gutenberg and available digitally for easy searching. The author of this blog, has developed a Twitter bot @LatinSynonyms that tweets periodically entries from this source for steady learning.
- De differentiis verborum by Popma is Latin-Latin dictionary now in a digital edtion. (also available in Latin-dict - see below)
- Gradus ad Parnassum contains synonyms for the words.