Referring to one that is extraordinary (8)
I believe the answer is:
singular
This clue is a double definition.
'referring to one' is the first definition.
(I've seen this before)
'extraordinary' is the second definition.
(similar in meaning)
'that is' acts as a link.
(Other definitions for singular that I've seen before include "Unique - nails rug (anag)" , "Atypical" , "Unusual, maybe unique" , "Individual; extraordinary" , "Odd; unique" .)