Sudden burst of extravagance (7)
I believe the answer is:
splurge
'sudden burst of extravagance' is the definition.
(I've seen this before)
This is the entire clue.
(Other definitions for splurge that I've seen before include "Sudden burst of extravagance" , "Not very well" , "lashing out" , "Spend wildly" , "Orgy" .)