Unfading (4)
I believe the answer is:
fast
'unfading' is the definition.
(I've seen this in another clue)
This is all the clue.
(Other definitions for fast that I've seen before include "Firm < moving rapidly" , "Refuse to eat - quickly" , "Sporting quickie?" , "Renounce food; quick" , "Quick - abstain from food" .)