Fossilized resin (5)
I believe the answer is:
amber
'fossilized 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 "first light" , "Light giving warning" , "The traffic-light between red and green" , "Fossil resin used in jewellery" , "gemstone" .)