Desert illusion (6)
I believe the answer is:
mirage
'desert illusion' is the definition.
(I've seen this in another clue)
This is the entire clue.
(Other definitions for mirage that I've seen before include "unreal" , "Illusory sighting" , "Deceptive image, in the desert say" , "You might see this in desert" , "Illusory image" .)