Con sordina, or con sordine
DEFINITION
(plural) with a mute, or with mutes; several orchestral instruments can have their tone muted with wood, rubber, metal, or plastic devices (for string instruments, mutes are clipped to the bridge, and for brass instruments, mutes are inserted in the bell); compare senza sordina in this list (which instructs the musicians to remove their mutes); see also Sordina. Note: sordina, with plural sordine, is strictly correct Italian, but the forms con sordino and con sordini are much more commonly used as terms in music.