Jazz trumpeter Davis (5)
I believe the answer is:
miles
'jazz trumpeter davis' is the definition.
(I've seen this in another clue)
This is all the clue.
(Other definitions for miles that I've seen before include "Distance units" , "'But I have promises to keep, and . . . . . to go before I sleep' (Frost)" , "Imperial units of length" , "a long way" .)