One's ugly feature (4)
I believe the answer is:
nose
'feature' is the definition.
(a facial feature)
'one's ugly' is the wordplay.
'ugly' indicates anagramming the letters (an ugly or wrong form of the letters).
'ones' is an anagram of 'NOSE'.
(Other definitions for nose that I've seen before include "front part of vehicle" , "scent" , "Pry" , "Snout" , "In-your-face" .)