A volcanic mountain (4)
I believe the answer is:
etna
'a volcanic mountain' is the definition.
(I've seen this in another clue)
This is all the clue.
(Other definitions for etna that I've seen before include "it may produce steam and ash" , "Natural hazard" , "Neat class of volcano in Sicily" , "Sicilian hothead?" , "Long-term smoker" .)