Odd fish perhaps not sharks (8)
I believe the answer is:
singular
This clue is a double definition.
'odd' is the first definition.
(I've seen this before)
'fish perhaps not sharks' is the second definition.
('sharks' is plural rather than singular)
(Other definitions for singular that I've seen before include "Remarkable - unique" , "Extraordinary - conspicuous - sole" , "Referring to one thing" , "As sheep may be, but not cattle or horses" , "Unique, peculiar" .)