Can containing one doubly fine meal (6)
I believe the answer is:
tiffin
'meal' is the definition.
(I know that tiffin is a type of meal)
'can containing one doubly fine' is the wordplay.
'can' becomes 'tin' (synonyms).
'containing' means one lot of letters goes inside another.
'one' becomes 'i' (Roman numeral).
'doubly' indicates the doubling of some letters.
'fine' becomes 'f' (abbreviation).
'f' duplicated is 'ff'.
'i'+'ff'='iff'
'tin' going around 'iff' is 'TIFFIN'.
(Other definitions for tiffin that I've seen before include "Light Indian repast" , "Midday meal for members of the British Raj in India" , "Anglo-Indian lunch" , "Snack, light meal (dated)" , "Indian midday meal" .)