Fossilized tree resin (5)
I believe the answer is:
'fossilized tree resin' is the definition.
(I've seen this in another clue)
This is all the clue.
(Other definitions for amber that I've seen before include "Colour of warning" , "Yellowish fossilised resin" , "Light colour between red and green" , "Cautionary signal" , ""Stop" traffic light" .)