Lover, one captured by pen in poetry? (5)
I believe the answer is:
swain
'lover' is the definition.
(old-fashioned term for a lover)
'one captured by pen in poetry?' is the wordplay.
'one captured by' indicates putting letters inside.
'pen' becomes 'swan' (pen is a female swan).
'in poetry?' becomes 'i' (I can't justify this - if you can you should give a lot more credence to this answer).
'swan' enclosing 'i' is 'SWAIN'.
Can you help me to learn more?
(Other definitions for swain that I've seen before include "lover of literature" , "Beau" , "Rustic suitor" , "Poetically, a young lover or suitor" , "Country boy" .)