Excessively abundant supply (4)
I believe the answer is:
glut
'excessively abundant supply' is the definition.
(I've seen this before)
This is all the clue.
(Other definitions for glut that I've seen before include "An excessive supply, maybe on the market" , "An excess of something so that prices fall" , "Excess, surfeit" , "Fill to excess" , "An excessive supply, just too much" .)