Figure a measure a certain success (5)
I believe the answer is:
cinch
'a certain success' is the definition.
The answer and definition can be both acts as well as being singular nouns.
Perhaps you can see an association between them that I can't see?
'figure a measure' is the wordplay.
'figure' becomes 'c' (I've seen this in other clues).
'a measure' becomes 'inch' (inch is a kind of measure).
'c'+'inch'='CINCH'
Can you help me to learn more?
(Other definitions for cinch that I've seen before include "simple job" , "Something easily done" , "piece of cake" , "A walk in the park" , "Doddle" .)