One's irregular feature (4)
I believe the answer is:
nose
'feature' is the definition.
(a facial feature)
'one's irregular' is the wordplay.
'irregular' is an anagram indicator.
'ones' with letters rearranged gives 'NOSE'.
(Other definitions for nose that I've seen before include "Deserving blame" , "Sense of smell; proceed cautiously" , "Grass" , "Facial organ" , "In-your-face" .)