Cliff can be frightening, just missing out on Yuletide's number one (4)
I believe the answer is:
scar
'cliff' is the definition.
(I've seen this in another clue)
I don't understand the remainder of the clue.
Can you help me to learn more?
(Other definitions for scar that I've seen before include "Injury mark - cliff" , "fall could possibly be the reason for one" , "Effect of unpleasant experience" , "brand" , "Permanent mark left by a wound" .)