A few days ago, I came accross Lingro, a very useful multilingual dictionary. The way to use this dictionary is explained in 3 steps on the Home Page:

The first 2 steps are straightforward: A URL is given and a translation mode is selected (For instance English -> French) and you just have to click on the word you want to translate to display the word definition/translation in a popup window. The third step offer the ability to record the word in a word list for future study.  This step is really interesting for learning as it allow to recall previous definition browsed. Of course registration is required for this part.