Plenty of money to back with (3)
I believe the answer is:
lot
'plenty' is the definition.
(thesaurus)
'money to back with' is the wordplay.
'money' becomes 'l' (L can mean 'pounds').
'back' indicates one should take the final letters.
'with' becomes 't' (I am not sure about this - if you are sure you should give a lot more credence to this answer).
The final letter of 'to' is 'o'.
'l'+'o'+'t'='LOT'
'of' acts as a link.
Can you help me to learn more?
(Other definitions for lot that I've seen before include "one whose wife should be remembered" , "Much at auction" , "crowd ..." , "In the Bible, his wife was turned into a pillar of salt" , "Genesis character" .)