A middling meal for one, possibly (8)
I believe the answer is:
luncheon
'a middling' is the definition.
Although both the answer and definition are singular nouns, I can't see how one could define the other.
'meal for one possibly' is the wordplay.
'meal' becomes 'lunch' (lunch is a kind of meal).
'for' is a charade indicator (letters next to each other).
'possibly' indicates an anagram.
'one' is an anagram of 'eon'.
'lunch'+'eon'='LUNCHEON'
Can you help me to learn more?
(Other definitions for luncheon that I've seen before include "Midday meal" , "midday menu" , "fare at one?" , "part of formal board" , "Food" .)