Instrument a semitone high? Not initially (4)
I believe the answer is:
harp
'instrument a semitone' is the definition.
'harp' can be an answer for 'instrument' (I've seen this before). I am unsure of the 'a semitone' bit.
'high? not initially' is the wordplay.
'high?' becomes 'sharp' (similar in meaning).
'not initially' means to remove the first letter.
'sharp' with its initial letter removed is 'HARP'.
Can you help me to learn more?
(Other definitions for harp that I've seen before include "Instrument for angel" , "David's instrument" , "semitone higher, abandoning intro" , "Traditional Gaelic musical instrument" , "Keep on about" .)