Unexpected flood under the bridge? (9)
I believe the answer is:
nosebleed
'bridge?' is the definition.
Although both the answer and definition are singular nouns, I can't see how one could define the other.
I cannot understand how the remainder of the clue works.
Can you help me to learn more?
(Other definitions for nosebleed that I've seen before include "Outpouring from snout" , "Epistaxis" , "Result of a punch on the schnozzle?" .)