Goes swiftly up for a violin (5)
I believe the answer is:
strad
'for a violin' is the definition.
(Stradivari abbreviation)
I don't understand how the rest of the clue works.
Can you help me to learn more?
(Other definitions for strad that I've seen before include "Old, very expensive violin (abbr)" , "Noted violin" , "musical instrument" , "Top-quality violin (abbr.)" , "that Grappelli could have played" .)