Possibly iron tin opener used during dinner (5)
I believe the answer is:
metal
'possibly iron tin opener' is the definition.
Although both the answer and definition are singular nouns, I can't see how they can define each other.
'used during dinner' is the wordplay.
'used' becomes 't' (I am not sure about this - if you are sure you should give a lot more credence to this answer).
'during' is an insertion indicator.
'dinner' becomes 'meal' (I've seen this in other clues).
't' placed inside 'meal' is 'METAL'.
Can you help me to learn more?
(Other definitions for metal that I've seen before include "Headbanger's music genre" , "Alloy" , "Gold or silver in heraldry" , "Zirconium, for example" , "Aluminium or copper for instance" .)