Unilluminated (5)
I believe the answer is:
unlit
'unilluminated' is the definition.
(I know that unilluminated can be written as unlit)
This is all the clue.
(Other definitions for unlit that I've seen before include "Not yet burning" , "not exactly bright" , "Shadowy" , "such as dark alley?" , "Dark, gloomy" .)