As he didn't want anyone else to hear what he was saying he spoke to her in a stage ...... (*) whisper (*) hush (*) voice (*) tone
This is a companion discussion topic for the original entry at https://english.best/questions/4440,as-he-didnt-want-anyone-else-to-hear-what-he-was-saying-he-spoke-to-her-in-a-stage-___/