Use your money to get by, as mentioned (3)
I believe the answer is:
buy
'use' is the definition.
Although both the answer and definition are singular nouns, I don't see how one could define the other.
I don't understand how the remainder of the clue works.
Can you help me to learn more?
(Other definitions for buy that I've seen before include "Purchase" , "Accept truth of (colloq.)" , "Get" , "Procure" .)