Wrote in confinement (6)
I believe the answer is:
penned
'wrote' is the definition.
('pen' can be a synonym of 'write')
I cannot understand how the remainder of the clue works.
Can you help me to learn more?
(Other definitions for penned that I've seen before include "Put down" , "Wrote; enclosed" , "Wrote; confined" , "Confined; written" , "in Reading Gaol, perhaps" .)