Unusual sort of moral ban (8)
I believe the answer is:
abnormal
'unusual' is the definition.
(similar in meaning)
'sort of moral ban' is the wordplay.
'sort of' is an anagram indicator.
'moral'+'ban'='moralban'
'moralban' is an anagram of 'ABNORMAL'.
(Other definitions for abnormal that I've seen before include "Different to what is ordinary or expected" , "Deviating from the usual" , "Odd" , "Irregular" , "The reverse of 32 Across" .)