Portly parrot underplays part (6)
I believe the answer is:
rotund
'portly' is the definition.
(I've seen this before)
'parrot underplays part' is the wordplay.
'part' indicates the answer is hidden within the clue.
'ROTUND' is hidden within 'parrot underplays'.
(Other definitions for rotund that I've seen before include "Chubby" , "Grandiloquent; podgy" , "'Corpulent, round (6)'" , "stout" , "Portly" .)