Home Counties captivated by aristocratic journalist's nasal outburst (9)
I believe the answer is:
nosebleed
'nasal outburst' is the definition.
Although both the answer and definition are singular nouns, I cannot see how they can define each other.
'home counties captivated by aristocratic journalist's' is the wordplay.
'home counties' becomes 'SE' (Home Counties in the South East of England).
'captivated by' indicates putting letters inside.
'aristocratic' becomes 'noble' (similar in meaning).
'journalist' becomes 'ed' (short for editor).
'se' placed within 'noble' is 'noseble'.
'noseble'+'ed'='NOSEBLEED'
Can you help me to learn more?
(Other definitions for nosebleed that I've seen before include "Epistaxis" , "Result of a punch on the schnozzle?" , "Outpouring from snout" .)