Ability to put a diet out (8)
I believe the answer is:
aptitude
'ability' is the definition.
(I know that aptitude is a type of ability)
'put a diet out' is the wordplay.
'out' indicates anagramming the letters (out can mean wrong or inaccurate).
'put'+'a'+'diet'='putadiet'
'putadiet' is an anagram of 'APTITUDE'.
'to' is the link.
(Other definitions for aptitude that I've seen before include "Update it, having natural skill" , "A natural talent or skill, for which there may be a test" , "Natural gift" , "Flair" , "fitness" .)