What is the best book to prepare for Ethics?

You can check out this website with the dictionary. Definitions are crisp

http://diyethics.com/dictionary/

You just copy the word list and search in the website. Content is good. 

Also for lexicon, dont buy lexicon, check out insights dictionary on ethics. It is good.

I have given the book reviews here, you can read it

https://forumias.com/post/detail/Prelims-Postponement-What-are-the-chances-of-Prelims-being-postponed-1585935026?JSxDLFItQzRgCmAK