Sternutation (6)
I believe the answer is:
sneeze
'sternutation' is the definition.
(I've seen this in another clue)
This is all the clue.
(Other definitions for sneeze that I've seen before include "Involuntary expiration of air" , "What might occasion a "Gesundheit"" , "Inadvertent explosion of air" , "Sternutation- see Zen (anag)" , "symptom of flu" .)