Exercise is able to make a nut (5)
I believe the answer is:
pecan
'a nut' is the definition.
(type of nut)
'exercise is able to' is the wordplay.
'exercise' becomes 'pe' (Physical Education).
'is able to' becomes 'can' (if you can do something you are able to do it).
'pe'+'can'='PECAN'
'make' is the link.
(Other definitions for pecan that I've seen before include "Walnut-like nut" , "US nut tree" , "nut-tree" , "Nutty type" , "Nut of American hickory tree" .)