500 at frozen arena effect hydration (5)
I believe the answer is:
drink
'effect hydration' is the definition.
Although both the answer and definition are singular nouns, I cannot understand how one could define the other.
'500 at frozen arena' is the wordplay.
'500' becomes 'D' (Roman numeral for 500).
'at' is a charade indicator (letters next to each other).
'frozen arena' becomes 'rink' (I am not sure about this - if you are sure you should give a lot more credence to this answer).
'd'+'rink'='DRINK'
Can you help me to learn more?
(Other definitions for drink that I've seen before include "Water" , "Beverage - alcohol" , "Possibly shake" , "effect rehydration" , "Swallow" .)