Antique barrel I can't store (5)
I believe the answer is:
relic
'antique' is the definition.
(I've seen this in another clue)
'barrel i can't store' is the wordplay.
'store' indicates a hidden word (I've seen 'stores' mean this).
'RELIC' is hidden within 'barrel i cant'.
(Other definitions for relic that I've seen before include "Surviving artefact" , "Corporal remains" , "E,g. dead saint's bone" , "Personal saintly memorial" , "Overshadow in importance" .)