Stack of bills (3)
I believe the answer is:
wad
'stack of bills' is the definition.
(I've seen this in another clue)
This is the entire clue.
(Other definitions for wad that I've seen before include "Bundle of soft material or of banknotes" , "Pad of loose material used for packing" , "Small mass of soft material" , "Small bundle" , "A bundle as of documents or banknotes" .)