Dull poet making a comeback (4)
I believe the answer is:
drab
'dull' is the definition.
('drab' can be a synonym of 'dull')
'poet making a comeback' is the wordplay.
'poet' becomes 'bard' (bard is a kind of poet).
'making a comeback' says the letters should be written in reverse.
'bard' in reverse letter order is 'DRAB'.
(Other definitions for drab that I've seen before include "Dull kind of bard" , "Cheerless, colourless" , "Gloomy" , "Colourless like bard" , "Cheerless, shabby" .)