Regrets holding key but frees from captivity (7)
I believe the answer is:
rescues
'frees from captivity' is the definition.
The definition and answer can be both to do with ownership as well as being verbs in their -s form.
Maybe you can see an association between them that I can't see?
'regrets holding key' is the wordplay.
'regrets' becomes 'rues' ('rue' can be a synonym of 'regret').
'holding' indicates putting letters inside.
'key' becomes 'esc' ('Escape' key on a computer keyboard).
'rues' placed around 'esc' is 'RESCUES'.
'but' acts as a link.
Can you help me to learn more?
(Another definition for rescues that I've seen is " Saves from danger".)