No rise for one in top form (6)
I believe the answer is:
senior
'one in top form' is the definition.
Both the definition and answer are adjectives. Perhaps you can see an association between them that I don't see?
'no rise' is the wordplay.
'no rise' anagrams to 'SENIOR'.
But, I'm not sure how the anagram is indicated.
'for' is the link.
Can you help me to learn more?
(Other definitions for senior that I've seen before include "Elder person - higher in rank" , "Pupil in a higher form" , "Higher in status" , "Denoting older people" , "Higher in rank or age" .)