The ISL has acquired the Oxford language dictionaries online. Arabic : Arabic-English. This dictionary, akin to an online version of the great Hans Wehr dictionary of modern Arabic has a total of 330, 000 words and more than 70, 000 examples of sentences.
A comprehensive dictionary that also offers grammar tips, it will surely be of great benefit to learners of Arabic.
The Oxford English-Arabic dictionary is accessible here as well as via the Islamic Studies and Middle East Studies Subject Guide.