Dry as dust (4)
I believe the answer is:
arid
'dry as dust' is the definition.
(I've seen this in another clue)
This is the entire clue.
(Other definitions for arid that I've seen before include "Very dry, having little rain" , "Dry raid" , "Lacking sufficient rainfall" , "Dry and unfertile" , "Dry and barren" .)