Release a fellow of one's own volition (4,4)
I believe the answer is:
free will
'own volition' is the definition.
'free will' can be an answer for 'volition' (I've seen this before). I'm unsure of the 'own' bit.
'release a fellow of one's' is the wordplay.
'release' becomes 'free' (synonyms).
'a fellow of one' becomes 'will' (I can't justify this - if you can you should believe this answer much more).
'free'+'will'='FREE-WILL'
Can you help me to learn more?
(Other definitions for free will that I've seen before include "ability to act without direction" , "discretion" , "Volition" , "Freedom of choice" , "autonomy" .)