In soft tones, so as not to be overheard; in an undertone: "There were aspersions cast, sotto voce, but knees quickly folded into curtsies when introductions were in order"(Barbara Lazear Ascher).
Music In very soft tones. Used chiefly as a direction.
[sot-oh voh-chee; It. sawt-taw vaw-che] 
