I think, unterschiedlich means just different to something else, whereas verschieden can stand sometimes for different things. e.g. das ist ja unterschiedlich which means it´s not the same or this is something different. Es gibt verschiedene Weisen, das zu machen this means there are many(different) manners to do it.

I don't know if there is a difference in the "dictionary definition" but to me as a native speaker, "verschieden" would be used when things are entirely different, and "unterschiedlich" means they have SOME differences but they are mostly the same.

Another thing I think would be that unterschiedlich is less specified than verschieden. As in, I am just speaking in general and not about the specific objects/subjects and their differences.

For example, my answer to the question, "Wann benutze Ich das Wort "unterschiedlich" und wann benutze Ich "verschieden?" would be "Das ist unterschiedlich." which is just a response that means, "it depends." I would not really say "das ist verschieden." because then I would have had to specify WHAT exactly is verschieden. Which two things? I hope this makes sense...