Finally fading, dim light (4)
I believe the answer is:
glow
'light' is the definition.
(I know that glow is a type of light)
'finally fading dim' is the wordplay.
'finally' indicates one should take the final letters.
'dim' becomes 'low' (as in a dim or low light).
The last letter of 'fading' is 'g'.
'g'+'low'='GLOW'
(Other definitions for glow that I've seen before include "Give out steady light" , "Shine steadily and brightly" , "rosy colour" , "Shine with warmth, emotion" , "Gleam" .)