Poem on a rude composition (7)
I believe the answer is:
rondeau
'poem' is the definition.
(I know that rondeau is a type of poem)
'on a rude composition' is the wordplay.
'composition' indicates an anagram (letters arranged or composed in a different order).
'on'+'a'+'rude'='onarude'
'onarude' anagrammed gives 'RONDEAU'.
(Other definitions for rondeau that I've seen before include "Style of poem" , "Poem of ten or thirteen lines" , "Short lyrical poem" , "Musical composition; poem of 13/15 lines" , "... and another" .)