One Look is an online dictionary with a difference. It allows you to type in a word and find not just one definition, but multiple definitions. In other words, it shows you the definition in a number of different dictionaries.
For example, a search for the word 'baroque' returns a list of 41 different definitions from both general dictionaries such as the Oxford, Websters etc and specialised art, business, computing and technology dictionaries.
One Look also has a Reverse Dictionary which allows you to search for a concept using a single word, a sentence or a question and receive a list of words and phrases related to that concept.
Powerful and useful stuff.