Sharp item on single fish (5,4)
I believe the answer is:
lemon sole
'fish' is the definition.
(I know that lemon sole is a type of sole)
'sharp item on single' is the wordplay.
'sharp item' becomes 'lemon' (I can't justify this - if you can you should give a lot more credence to this answer).
'on' is a charade indicator (letters next to each other).
'single' becomes 'sole' (similar in meaning).
'lemon'+'sole'='LEMON-SOLE'
Can you help me to learn more?
(Other definitions for lemon sole that I've seen before include "fish to eat" , "Lose melon, find kind of plaice" , "Another tasty flatfish like lone citrus fruit" , "swimmer" , "Flatfish, valued as food" .)