Dull poet rejected (4)
I believe the answer is:
'dull' is the definition.
(similar in meaning)
'poet rejected' is the wordplay.
'poet' becomes 'bard' (bard is a kind of poet).
'rejected' is a reversal indicator.
'bard' back-to-front is 'DRAB'.
(Other definitions for drab that I've seen before include "Lacklustre" , "Cheerless, colourless" , "Shabby; a slattern (arch.)" , "Dull and boring" , "Drearily dull; slattern" .)