I opened Girdlestone's Synonyms of the Old Testament, because I wanted to see his discussion of a Hebrew word. So I scrolled down to the appendix, or index of Hebrew words, to find the pages he discusses it, but there was no index included. I looked at Trench's Synonyms and the same thing.
I know there must be other ways to find this information, but it just seems basic to me that if you scan a book, you would scan all the indices and appendices as well. I am very disappointed.