Greeting the onset of spring with a musical instrument (6)
I believe the answer is:
salute
'greeting' is the definition.
(salute is a kind of greeting)
'the onset of spring with a musical instrument' is the wordplay.
'the onset of' says to take the initial letters.
'with' means one lot of letters go next to another.
'musical instrument' becomes 'lute' (lute is a kind of musical instrument**).
The initial letter of 'spring' is 's'.
's'+'a'+'lute'='SALUTE'
(Other definitions for salute that I've seen before include "Acknowledge (superior)" , "Greet in military fashion" , "Greet in military style" , "Mark" , "Ceremonial firing of guns" .)