I was surfing the net (checking out this blog by Seth Dickens) and I found out about this new online dictionary: MacMillan Open Dictionary.
As Erica Ho puts it: "Macmillan's new Open Dictionary allows anyone to suggest definitions for new words, similar to online Urban Dictionary. It differs in the fact that the definitions are carefully screened and handpicked, making it—in theory—more reliable and trustworthy. Language is a living thing, and constantly changing. Open Dictionary features a host of current buzzwords, from neologisms to slang. Because the definitions are edited by Macmillan, explanations are clear and easy to understand". I've just added it to the right menu dictionaries. Have a look!