Dreary poet rejected (4)
I believe the answer is:
drab
'dreary' is the definition.
('drab' can be a synonym of 'dreary')
'poet rejected' is the wordplay.
'poet' becomes 'bard' (bard is a kind of poet).
'rejected' is a reversal indicator.
'bard' backwards is 'DRAB'.
(Other definitions for drab that I've seen before include "Of a dull greenish-brown colour" , "Sombre" , "Drearily dull; slattern" , "Grey or light brown cloth" , "Cheerless, shabby" .)