Dreary poet returns (4)
I believe the answer is:
drab
'dreary' is the definition.
(I know that dreary can be written as drab)
'poet returns' is the wordplay.
'poet' becomes 'bard' (bard is a kind of poet).
'returns' is a reversal indicator.
'bard' written backwards gives 'DRAB'.
(Other definitions for drab that I've seen before include "Lacking brightness or colour" , "Dull - dreary" , "woman with slatternly habits" , "kind of tart" , "Not cheering" .)