Not shiny (5)
'not shiny' 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 record two images on same film" , "Mask used to block out areas of the image in filming" , "A dull finish" , "Mask used in film; ET mat (anag.)" , "Dull, flat" .)
(Other definitions for dull that I've seen before include "Lacking brightness" , "Constable?" , "mat" , "Cloudy or boring" , "Overcast or uninteresting" .)