Dull poet taken up (4)
I believe the answer is:
drab
'dull' is the definition.
(synonyms)
'poet taken up' is the wordplay.
'poet' becomes 'bard' (bard is a kind of poet).
'taken up' 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 sort of bard" , "Cheerless, shabby" , "kind of tart" , "Dull and monotonous" , "Cheerless, colourless" .)