Possibly stainless tin opener used during a meal (5)
I believe the answer is:
metal
'possibly stainless' is the definition.
(I know that stainless steel is a type of alloy steel)
'tin opener used during a meal' is the wordplay.
'opener' indicates taking the first letters.
'used during' means one lot of letters goes inside another.
The initial letter of 'tin' is 't'.
't' inserted into 'meal' is 'METAL'.
(Other definitions for metal that I've seen before include "Conducting solid" , "Zirconium, for example" , "Copper possibly" , "barium?" , "Copper, perhaps" .)