Gloomy poet retires (4)
I believe the answer is:
drab
'gloomy' is the definition.
(I know that gloomy can be written as drab)
'poet retires' is the wordplay.
'poet' becomes 'bard' (bard is a kind of poet).
'retires' is a reversal indicator.
'bard' written backwards gives 'DRAB'.
(Other definitions for drab that I've seen before include "Of a dull greenish-brown colour" , "Dull and colourless" , "woman with slatternly habits" , "Dingy - shabby" , "Lacklustre" .)