Great African desert (6)
I believe the answer is:
sahara
'great african desert' is the definition.
(I've seen this before)
This is all the clue.
(Other definitions for sahara that I've seen before include "Hottest desert" , "About 3,500,000 square miles of Africa" , "World's largest desert" , "North African desert" , "Uncultivated region of north Africa" .)