In the barrel I can fill what’s left over (5)
I believe the answer is:
relic
'left over' is the definition.
Although both the answer and definition are singular nouns, I cannot see how one could define the other.
'in the barrel i can fill' is the wordplay.
'in' says the answer is hidden in the clue.
'RELIC' is hidden within 'barrel i can fill'.
'what's' is the link.
Can you help me to learn more?
(Other definitions for relic that I've seen before include "Venerated remains" , "Heirloom" , "Item surviving from the past" , "Souvenir; survival" , "Fossil" .)