Latin poet breaking promise (9)
I believe the answer is:
potential
'promise' is the definition.
(thesaurus)
'latin poet breaking' is the wordplay.
'breaking' indicates an anagram.
'latin'+'poet'='latinpoet'
'latinpoet' with letters rearranged gives 'POTENTIAL'.
(Other definitions for potential that I've seen before include "Powerful" , "Budding" , "Latent talent" , "Inherent capacity not realised" , "Possibility, promise" .)