Threatening, disquieting (4)
I believe the answer is:
ugly
I believe this clue is a double definition.
'threatening' is the first definition.
(synonyms)
'disquieting' is the second definition.
(I've seen this before)
(Other definitions for ugly that I've seen before include "offensive to look at" , "Not nice-looking" , "Evil-looking" , "Difficult to look at" , "Not pleasing to look at" .)