Indulge, oddly, poetaster's ending — his work's limited (5)
I believe the answer is:
idler
'his work's limited' is the definition.
(an idler doesn't do much work)
'indulge oddly poetaster's ending' is the wordplay.
'oddly' means one should take alternating letters (letters in the odd-numbered positions are used).
'ending' indicates one should take the final letters.
The final letter of 'poetaster' is 'r'.
The alternating letters of 'indulge' are 'idle'.
'idle'+'r'='IDLER'
(Other definitions for idler that I've seen before include "Layabout; Dr Johnson essay series" , "Time waster" , "Lollard" , "Bum" , "Work-shy individual" .)