Pledge of bloke to suppress an outburst (8)
I believe the answer is:
guaranty
'pledge' is the definition.
(thesaurus)
'bloke to suppress an outburst' is the wordplay.
'bloke' becomes 'guy' (I've seen this before).
'to suppress' indicates putting letters inside.
'an' becomes 'a'.
'outburst' becomes 'rant' (I have seen 'Angry outburst ' mean 'rant' so perhaps 'outburst' could also mean 'rant').
'a'+'rant'='arant'
'guy' going around 'arant' is 'GUARANTY'.
'of' acts as a link.
(Other definitions for guaranty that I've seen before include "security" , "Agreement to answer for another's debts" , "Agreement backed by collateral" .)