Instrument could indicate hail, given another tap (5)
I believe the answer is:
cello
'instrument' is the definition.
(cello is a kind of instrument)
I cannot understand how the rest of the clue works.
(Other definitions for cello that I've seen before include "Orchestral instrument played between the legs" , "large-scale fiddle" , "Viola's bigger brother?" , "Played by Rostropovich" , "Bowed musical instrument" .)