Small instrument not blunt (5)
I believe the answer is:
sharp
'not blunt' is the definition.
(I've seen this before)
'small instrument' is the wordplay.
I cannot really understand how this works, but
'small' could be 's' (abbreviation - e.g. clothes size) and 's' is located in the answer.
'instrument' could be 'harp' (harp is a kind of instrument) and 'harp' is present in the answer.
No letters remain.
This may be the basis of the clue (or it may be nonsense).
Can you help me to learn more?
(Other definitions for sharp that I've seen before include "Acute; pointed" , "Cutting; note" , "Bitter" , "Mentally acute" , "Tangy" .)