Not finished during a meal, it may well be hard (5)
I believe the answer is:
metal
'it may well be hard' is the definition.
The definition suggests a singular noun which matches the answer.
'not finished during a meal' is the wordplay.
'not finished' becomes 't' (I am not sure about this - if you are sure you should believe this answer much more).
'during' means one lot of letters goes inside another.
't' going into 'meal' is 'METAL'.
Can you help me to learn more?
(Other definitions for metal that I've seen before include "Lead, say" , "Iron, gold or silver, for example" , "Alloy" , "Intrinsic quality; stone for roads" , "Conducting solid" .)