Ugly blemish causing endless fright (4)
I believe the answer is:
scar
'ugly blemish' is the definition.
'scar' can be an answer for 'blemish' (I've seen this before). I am unsure of the 'ugly' bit.
'endless fright' is the wordplay.
'endless' means to remove the last letter.
'fright' becomes 'scare' (synonyms).
'scare' with its final letter removed is 'SCAR'.
'causing' acts as a link.
Can you help me to learn more?
(Other definitions for scar that I've seen before include "Craggy rock formation" , "Effect of unpleasant experience" , "Mark left on healed tissue" , "fall could possibly be the reason for one" , "Injury mark - cliff" .)