Greet Salvation Army instrument (6)
I believe the answer is:
salute
'greet' is the definition.
(I know that salute is a kind of greet)
'salvation army instrument' is the wordplay.
'salvation army' becomes 'SA' (abbreviation).
'instrument' becomes 'lute' (lute is a kind of instrument).
'sa'+'lute'='SALUTE'
(Other definitions for salute that I've seen before include "Hail respectfully" , "Pay tribute to; greet" , "Hail with a gesture" , "Military gesture of respect" , "Greet in a friendly way" .)