Outburst from girlfriend over sweetheart (4)
I believe the answer is:
gale
'outburst' is the definition.
(thesaurus)
'girlfriend over sweetheart' is the wordplay.
'girlfriend' becomes 'gal' (gal can informally mean a girlfriend).
'over' means one lot of letters go next to another.
'sweetheart' becomes 'e' (the heart/centre of 'sweet').
'gal'+'e'='GALE'
'from' acts as a link.
(Other definitions for gale that I've seen before include "Strong wind" , "Squall" , "High wind" , "Force 8 wind" , "Bille from a bladder" .)