Dull send-up of Shakespeare? (4)
I believe the answer is:
drab
'dull' is the definition.
(synonyms)
'send-up of shakespeare?' is the wordplay.
'send-up of' says the letters should be written backwards.
'shakespeare?' becomes 'bard' (Shakespeare is known as the Bard).
'bard' backwards is 'DRAB'.
(Other definitions for drab that I've seen before include "Dull and colourless" , "Cheerless, colourless" , "Dull light brown colour" , "Colourless kind of bard" , "Dingy - shabby" .)