Introduction to rondeau penned by terrible poet (4)
I believe the answer is:
bard
'poet' is the definition.
(I know that bard is a type of poet)
'introduction to rondeau penned by terrible' is the wordplay.
'introduction to' says to take the initial letters.
'penned by' is an insertion indicator (inserted letters are penned in).
'terrible' becomes 'bad' (similar in meaning).
The initial letter of 'rondeau' is 'r'.
'r' inserted inside 'bad' is 'BARD'.
(Other definitions for bard that I've seen before include "Epic poet" , "Animal; cruel person" , "Poet - prophet" , "Celtic poet" , "Gray, perhaps" .)