Sound of a sneeze (7)
I believe the answer is:
atishoo
'sound of a sneeze' is the definition.
(I've seen this before)
This is all the clue.
(Other definitions for atishoo that I've seen before include "Sudden eruption" , "Sneezing sound" , "report of involuntary escape from trap?" , "Sound of explosion" , "Sound of a sneeze" .)