Fifty-four letters for something to eat (5)
I believe the answer is:
liver
'something to eat' is the definition.
(liver is a kind of food)
'fifty-four letters' is the wordplay.
'fifty' becomes 'L' (Roman numeral).
'four' becomes 'IV' (Roman numerals).
'letters' becomes 'er' (I can't justify this - if you can you should give a lot more credence to this answer).
'l'+'iv'+'er'='LIVER'
'for' is the link.
Can you help me to learn more?
(Other definitions for liver that I've seen before include "Glandular organ of the stomach" , "Bile-secreting organ" , "Internal organ" , "Abdominal organ" , "Dark reddish brown" .)