BusinessDictionary.com was recently launched. You can use it to look up over 20,000 business-related words.
The terms are broken down by categories, so you can browse (helps if you are not sure of the exact word or phrase). They have a word look-up box you can embed into your website.
There’s even a “word of the day” app for Facebook — because having a Facebook application is becoming de rigueur for any Web product these days.
I find myself often going to Wikipedia to look up business phrases or industry terms-of-art. However, I usually end up with far more information than I need. BusinessDictionary.com looks like it could be a better alternative to Wikipedia for quick look-ups.