Sudden eruption - and, reportedly, what might stifle it? (7)
I believe the answer is:
'sudden eruption' is the definition.
(I've seen this before)
I don't understand how the remainder of the clue works.
(Other definitions for atishoo that I've seen before include "report of involuntary escape from trap?" , "hay-fever sufferer may interject this" , "25 sound" , "Sound of explosion" , "Sound of a sneeze" .)