Oversupply of goods — loss upsets trader initially (4)
I believe the answer is:
glut
'oversupply' is the definition.
('glut' can be a synonym of 'oversupply')
'goods loss upsets trader initially' is the wordplay.
'initially' suggests taking the first letters.
The first letters of 'goods loss upsets trader' is 'GLUT'.
'of' is the link.
(Other definitions for glut that I've seen before include "stuff" , "Overabundance" , "An excessive supply or surfeit" , "Flood" , "Oversupply, plethora" .)