Part of warehouse receipt for consumer (4)
I believe the answer is:
Here is my best explanation:
'consumer' is the definition.
(user is a kind of consumer)
'part of warehouse receipt for' is the subsidiary indication.
'part of' indicates a hidden word.
'user' is hidden within 'warehouse receipt for'.
(Other definitions for user that I've seen before include "One exploiting others", "One who exploits others", "Drug addict (informal)", "One operating something", "Person employing something", "Ruse (anag.)", "Consumer", "Operator; exploiter", "Drug-taker" and "Person who takes drugs".)