Strange but unique (8)
I believe the answer is:
singular
I believe this is a double definition.
'strange' is the first definition.
(similar in meaning)
'unique' is the second definition.
(I know that unique can be written as singular)
'but' is the link.
(Other definitions for singular that I've seen before include "Extraordinary - just one (8)" , "number" , "Unusual - not plural" , "Individual; extraordinary" , "Atypical" .)