Most unsightly (7)
I believe the answer is:
ugliest
'most unsightly' is the definition.
('ugly' can be similar in meaning to 'unsightly')
This is all the clue.
(Other definitions for ugliest that I've seen before include "Least pretty" , "superlatively unattractive" , "Most deficient in beauty" , "Most unattractive in appearance" , "Least attractive" .)