Unison shown by soldiers during a salute (9)
I believe the answer is:
agreement
'unison' is the definition.
(thesaurus)
'soldiers during a salute' is the wordplay.
'soldiers' becomes 'men' (I've seen this before).
'during' indicates putting letters inside.
'salute' becomes 'greet' (I've seen this before).
'a'+'greet'='agreet'
'men' inserted into 'agreet' is 'AGREEMENT'.
'shown by' acts as a link.
(Other definitions for agreement that I've seen before include "consensus" , "legal contract maybe" , "Pact" , "deal" , "Correspondence" .)