There's enough slang within the English language to make up a whole new language. If you need to do some research for an English assignment, or you're just into linguistics, this online dictionary is your best bet. Green's Dictionary of Slang is an award-winning set of books that is widely considered the best English slang reference out there (sorry Urban Dictionary). The reference is the largest of its kind, and contains nearly 100,000 words supported by over 400,000 citations that go all the way back to the middle ages. If you ever need to do any research on slang terms in the English language, you can't beat Green's -- and now it's available online.
If you wanted to look up some words in Green's before, you'd have to hit up your local library or pay a hefty price for your own set of books. Now you can do all your research with their online dictionary for free. And because it's all now online, they will be able to constantly update it as new slang comes into play. Check it out at the link below.