Mirage subject (5)
I believe the answer is:
oasis
'mirage subject' is the definition.
(I've seen this in another clue)
This is the entire clue.
(Other definitions for oasis that I've seen before include "British band" , "Q-and-A game" , "place of relief" , "Pop group" , "Band with Liam and Noel Gallagher" .)