Gmail Thesaurus

Isn't it time that Gmail added a simple thesaurus to their email client. I don't know why but for some reason it is very difficult to find dictionaries in applications on a desktop or within Web Applications. I know one can just use something like Answers.com or Dictionary.com but what if I am working offline?

So much so that even MS Word, to my knowledge, doesn't have a means of finding the meaning of a word (the true essence of a dictionary) by default. Google through social networking techniques may even be able to come up with what I would call a social dictionary whereby it learns from people's language like the search function's ability to suggest correct spellings.