Prodigal (11)
I believe the answer is:
spendthrift
'prodigal' is the definition.
(I know that spendthrift is a type of prodigal)
This is the entire clue.
(Other definitions for spendthrift that I've seen before include "Extravagantly spending person" , "Irresponsible user of money" , "Prodigal" , "Wastrel" , "Squanderer" .)