EU leaders stand up to suppress very loud outburst (8)
I believe the answer is:
effusion
'outburst' is the definition.
(I know that outburst can be written as effusion)
'eu leaders stand up to suppress very loud' is the wordplay.
'leaders' suggests taking the first letters.
'up to' becomes 'ion' (I am not sure about this - if you are sure you should give a lot more credence to this answer).
'suppress' is an insertion indicator.
'very loud' becomes 'ff' (musical abbreviation).
The initial letter of 'stand' is 's'.
'eu'+'s'+'ion'='eusion'
'eusion' going around 'ff' is 'EFFUSION'.
Can you help me to learn more?
(Other definitions for effusion that I've seen before include "Piece of unrestrained writing" , "Unrestrained outpouring" , "Gush" , "A pouring forth of thought or feeling" , "Outpouring (of words?)" .)