Advance position is material (9)
I believe the answer is:
substance
'is material' is the definition.
(I've seen this before)
'advance position' is the wordplay.
'advance' becomes 'sub' (both can mean a loan).
'position' becomes 'stance' (stance is a kind of position).
'sub'+'stance'='SUBSTANCE'
(Other definitions for substance that I've seen before include "Property" , "Basic matter" , "Physical material" , "Matter or material that a thing is made of" , "Physical matter" .)