1 Without variety or features, e.g. a blank unrelieved wall.
2 Aperture that is blind, that is sealed up, e.g. a blocked-up window, or an opening looking like a window, but actually blind.
3 Flat or dull, without brilliance, as in finishes.
4 Useless, or not used for its original purpose, e.g. a chimney-flue.