Aridity (7)
I believe the answer is:
dryness
'aridity' is the definition.
(I've seen this in another clue)
This is all the clue.
(Other definitions for dryness that I've seen before include "Lack of moisture" , "Freedom from moisture" , "producing thirst" , "Characteristic of some wines" , "Matter-of-fact quality (of humour)" .)