Lacking luster (5)
I believe the answer is:
matte
'lacking luster' is the definition.
(I've seen this in another clue)
This is the entire clue.
(Other definitions for matte that I've seen before include "Mask used to block out areas of the image in filming" , "Mask used to record two images on same film" , "Dull, flat" , "Mask used to add an image in front of camera" , "A dull finish" .)