We've got some dictionaries that you can use in the library (in print) and we have some that you can access electronically from anywhere!
Wikipedia is a great source of background information. The worry by some librarians and professors is that there is little control over changes made to entries. That being said, Wikipedia can be still be a useful tool. I like to use it for the suggestions for further reading and looking at the reference section (just like reading any article, the references can sometimes be the best part).
Check out the Physics Portal from Wikipedia.