Adult food store is a top-class investment (4-4,5)
I believe the answer is:
blue-chip stock
'adult food' is the definition.
Although both the answer and definition are singular nouns, I cannot understand how they can define each other.
'store is a top-class investment' is the wordplay.
I cannot quite understand how this works, but
'store' could be 'stock' (synonyms) and 'stock' is present in the answer.
'investment' could be 'bluechip' (I have seen 'certain investment' mean 'blue chip' so perhaps 'investment' could also mean 'blue chip') and 'bluechip' is found within the answer.
No letters remain.
This may be the basis of the clue (or it may be nonsense).
Can you help me to learn more?