Rook caged by wicked poet (4)
I believe the answer is:
bard
'poet' is the definition.
(I know that poet can be written as bard)
'rook caged by wicked' is the wordplay.
'rook' becomes 'R' (chess abbreviation).
'caged by' is an insertion indicator.
'wicked' becomes 'bad' (similar in meaning).
'r' put into 'bad' is 'BARD'.
(Other definitions for bard that I've seen before include "Celtic poet" , "Gray, perhaps" , "Traditional poet" , "Epic poet" , "Ancient poet" .)