Swimmer winning medal initially for his swimming (8)
I believe the answer is:
goldfish
'swimmer winning' is the definition.
Although both the answer and definition are singular nouns, I cannot see how they can define each other.
'medal initially for his swimming' is the wordplay.
'medal' becomes 'gold' (I am not sure about this - if you are sure you should give a lot more credence to this answer).
'initially' says to take the initial letters.
'swimming' indicates anagramming the letters.
The first letter of 'for' is 'f'.
'his' is an anagram of 'ish'.
'gold'+'f'+'ish'='GOLDFISH'
Can you help me to learn more?
(Other definitions for goldfish that I've seen before include "Orange-red freshwater fish" , "Bowl or pond dweller" , "one enjoying pond life?" , "Pond or aquarium fish" , "he may go round in a tank" .)