Impersonation of outburst by operatic heroine (7)
I believe the answer is:
mimicry
'impersonation' is the definition.
(I know that mimicry is a type of impersonation)
'outburst by operatic heroine' is the wordplay.
'outburst' becomes 'cry' (cry is a kind of outburst).
'by' means one lot of letters go next to another.
'operatic heroine' becomes 'mimi'.
'cry' put after 'mimi' is 'MIMICRY'.
'of' is the link.
(Other definitions for mimicry that I've seen before include "Imitation" , "Copycat behaviour" , "Parody" , "Skill of copying another" , "Taking off" .)