Spendthrift pair with gold becoming spoilt (8)
I believe the answer is:
prodigal
'spendthrift' is the definition.
('prodigal' can be similar in meaning to 'spendthrift')
'pair with gold becoming spoilt' is the wordplay.
'with' says to put letters next to each other.
'becoming spoilt' indicates an anagram.
'pair'+'gold'='pairgold'
'pairgold' anagrammed gives 'PRODIGAL'.
(Other definitions for prodigal that I've seen before include "Extravagant - lavish" , "Grip load (anag.)" , "Profligate" , "Wasting money" , "Squandering" .)