Milk or paint, possibly (5)
I believe the answer is:
pinta
'milk' is the definition.
Both the answer and definition are singular nouns.
Perhaps there's an association between them I don't understand?
'paint possibly' is the wordplay.
'possibly' indicates an anagram.
'paint' with letters rearranged gives 'PINTA'.
'or' is the link.
Can you help me to learn more?
(Other definitions for pinta that I've seen before include "vessel for Columbus?" , "early delivery?" , "Bottle of milk" , "drink" , "Columbus's ship - some milk!" .)