Of a surface, finish, etc.: without lustre, dull; unpolished. Of a paint, varnish, etc.: imparting a dull finish.

(un-, prefix1 affix 1.)

Of pigments and painted surfaces: Dead, dull, without gloss.

transferred. Of paint, lacquer, or varnish: lustreless, dull. (Cf. C. 12, flat, v.2 8a, flatted, adj.1 5.)