I have just come across a very interesting English-Arabic online dictionary, and I would like to tell you about it. It is a free online tool which I found to be very useful. Here is the website:

http://www.arabdict.com/en/

I have tried it myself, and it is great! It enjoys many interesting features!

It suggests ways to complete the word you type.

It presents expressions like idioms and collocations in which the word is used.

It presents a wide variety of meanings, and other related words from the same root.

It is really great, and free! I hope you find it useful!