Jam picked up in supermarket (3)
I believe the answer is:
ram
'jam' is the definition.
('ram' can be a synonym of 'jam')
'picked up in supermarket' is the wordplay.
'picked up' is a reversal indicator.
'in' indicates a hidden word.
'mar' is hidden within 'supermarket'.
'mar' reversed gives 'RAM'.
(Other definitions for ram that I've seen before include "Butt" , "Aggressive sheep?" , "'Computer memory, initially (3)'" , "needed for PC" , "what comes after fish" .)