Unusual, atypical (8)
I believe the answer is:
abnormal
This clue is a double definition.
'unusual' is the first definition.
(similar in meaning)
'atypical' is the second definition.
(similar in meaning)
(Other definitions for abnormal that I've seen before include "Deviant or unnatural" , "Moral ban (anag.)" , "'Aberrant, atypical (8)'" , "Deviating from the standard" , "Extraordinary" .)