Exercise? It is embraced by poet mostly for fitness (8)
I believe the answer is:
aptitude
'fitness' is the definition.
(thesaurus)
'exercise? it is embraced by poet mostly' is the wordplay.
'exercise?' becomes 'pt'.
'is embraced by' means one lot of letters goes inside another.
'poet mostly' becomes 'aude' (I am not sure about this - if you are sure you should believe this answer much more).
'pt'+'it'='ptit'
'ptit' placed into 'aude' is 'APTITUDE'.
'for' is the link.
Can you help me to learn more?
(Other definitions for aptitude that I've seen before include "Natural gift" , "Update it, having natural skill" , "A particular talent or facility" , "Bent" , "Update it, having a relevant talent" .)