Instrument initially very intimidating, one loves it now (6)
'instrument' is the definition.
(violin is a kind of instrument)
'initially very intimidating one loves it now' is the wordplay.
'initially' suggests taking the first letters.
The initial letters of 'very intimidating one loves it now' is 'VIOLIN'.
(Other definitions for violin that I've seen before include "A stringed musical instrument, say a Stradivarius", "Instrument with bow", "Menuhin's instrument", "It'a played with a bow", "Nigel Kennedy instrument".)