Dull poet is sent up (4)
I believe the answer is:
drab
'dull' is the definition.
(synonyms)
'poet is sent up' is the wordplay.
'poet' becomes 'bard' (bard is a kind of poet).
'is sent up' is a reversal indicator.
'bard' reversed gives 'DRAB'.
(Other definitions for drab that I've seen before include "Grey or light brown cloth" , "Dull and monotonous" , "Shabby; a slattern (arch.)" , "Of a dull greenish-brown colour" , "Dowdy" .)