Explosion somewhere under the bridge? (6)
I believe the answer is:
sneeze
'bridge?' is the definition.
Although both the answer and definition are singular nouns, I can't see how they can define each other.
I can't explain the rest of the clue.
Can you help me to learn more?
(Other definitions for sneeze that I've seen before include "Expel air from nose" , "Response to nasal irritation" , "See Zen at the sign of a cold" , "coming from cold" , "involuntary reaction" .)