Poorly rate poet's musical work (8)
I believe the answer is:
operetta
'musical work' is the definition.
(I've seen this before)
'poorly rate poet's' is the wordplay.
'poorly' indicates an anagram (I've seen this in other clues).
'rate'+'poet'='ratepoet'
'ratepoet' with letters rearranged gives 'OPERETTA'.
(Other definitions for operetta that I've seen before include "A short or light musical comedy like those of G & S" , "light-hearted performance" , "La belle Helene, say" , "G&S production, perhaps" , "piece of music?" .)