Dissent shown by American gangster meeting official (7)
I believe the answer is:
refusal
'dissent' is the definition.
(I've seen this before)
'american gangster meeting official' is the wordplay.
'american' becomes 'us' (abbreviation for United States).
'gangster' becomes 'al' (Al Capone).
'meeting' says to put letters next to each other.
'official' becomes 'ref' (match official in football, say).
'us'+'al'='usal'
'usal' after 'ref' is 'REFUSAL'.
'shown by' is the link.
(Other definitions for refusal that I've seen before include "maybe never" , "First this is first choice before others" , "Repudiation" , "problem for a show-jumper" , "Turning-down; denial" .)