Excellent prize fund, mine after retirement (6)
I believe the answer is:
tiptop
'excellent' is the definition.
(I've seen this before)
'prize fund mine after retirement' is the wordplay.
'prize fund' becomes 'pot' (as in a jackpot).
'mine' becomes 'pit' (down the pit).
'after retirement' says the letters should be written in reverse.
'pot'+'pit'='potpit'
'potpit' in reverse letter order is 'TIPTOP'.
(Other definitions for tiptop that I've seen before include "Informally excellent, very best" , "Capital" , "The height of excellence" , "Quality" , "Best of its kind" .)