Dull bit of condiment (3)
I believe the answer is:
dim
'dull' is the definition.
(I know that dull can be written as dim)
'bit of condiment' is the wordplay.
'bit of' indicates the answer is hidden within the clue.
'DIM' is hidden within 'condiment'.
(Other definitions for dim that I've seen before include "Slow to learn" , "Not clear or not too bright" , "Not bright, literally or mentally" , "Sombre" , "Providing little light" .)