Want expensive trough cleaned out (6)
I believe the answer is:
dearth
'want' is the definition.
(both can mean a lack or scarcity)
'expensive trough cleaned out' is the wordplay.
'expensive' becomes 'dear' (similar in meaning).
'cleaned out' suggests removing the centre.
'trough' with its centre removed is 'th'.
'dear'+'th'='DEARTH'
(Other definitions for dearth that I've seen before include "want" , "Acute shortage" , "Shortage, paucity" , "Scarcity of thread" , "Scarcity - famine" .)