Small instrument pitched too high (5)
I believe the answer is:
sharp
'pitched too high' is the definition.
(I've seen this in another clue)
'small instrument' is the wordplay.
I cannot really see how this works, but
'small' could be 's' (abbreviation - e.g. clothes size) and 's' is found in the answer.
'instrument' could be 'harp' (harp is a kind of instrument) and 'harp' is located 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 "Acidic; note" , "Not blunt" , "Tangy" , "Unscrupulous character" , "Keen-edged" .)