Most athletic fellow takes it before exam (7)
I believe the answer is:
fittest
'most athletic' is the definition.
Both the answer and definition are superlative adjectives. Perhaps you can see a link between them that I don't see?
'fellow takes it before exam' is the wordplay.
'fellow' becomes 'F' (abbreviation - of a society etc.).
'takes' is a charade indicator (letters next to each other).
'before' means one lot of letters go next to another.
'exam' becomes 'test' (synonyms).
'f'+'it'+'test'='FITTEST'
Can you help me to learn more?
(Other definitions for fittest that I've seen before include "most sound" , "'Survival of the - - '" , "superlatively healthy" , "Healthiest" , "Most suitable" .)