Can I manually upgrade/enhance/optimize MS Word's plain-Jane thesaurus?

MS Word’s thesaurus can be handy when one is in a pinch, but it’s rather limited, inadequate, incomplete and narrow.

Does someone know of a feature, cheat or tweak that would allow users to dump a few thousand additional synonyms (and slang/foreign expressions) into the reference core?

If there is a better computer-based thesaurus, I’m all ears.

You can purchase any number of add-on thesauruses and dictionaries for Word. There are even a few freeware versions floating around.