Sign of things to come (4)
I believe the answer is:
omen
'sign of things to come' is the definition.
(I've seen this in another clue)
This is all the clue.
(Other definitions for omen that I've seen before include "Augur" , "Auspice" , "Sign of likely future event" , "Harbinger, portent" , "writing on the wall" .)