A cold one, four-fifths ice? (5)
I believe the answer is:
drink
'a cold one four-fifths ice?' is the definition.
The answer and definition can be both things that one consumes for nourishment as well as being singular nouns.
Perhaps they are linked in a way I don't understand?
'fifths ice?' is the wordplay.
'fifths' becomes 'd' (I am not sure about this - if you are sure you should give a lot more credence to this answer).
'ice?' becomes 'rink' (ice is a kind of rink).
'd'+'rink'='DRINK'
Can you help me to learn more?
(Other definitions for drink that I've seen before include "Booze" , "Beverage - alcohol" , "effect rehydration" , "Liquid refreshment" , "Demon beverage?" .)