Nouns

(n)mute, deaf-mute, deaf-and-dumb persona deaf person who is unable to speak
(n)mutea device used to soften the tone of a musical instrument

Verbs

(v)muffle, mute, dull, damp, dampen, tone downdeaden (a sound or noise), especially by wrapping

Adjectives

(s)mute, tongueless, unspoken, wordless, silentexpressed without speech“a mute appeal”, “a silent curse”, “best grief is tongueless” (Emily Dickinson), “the words stopped at her lips unsounded”, “unspoken grief”, “choking exasperation and wordless shame” (Thomas Wolfe)
(s)dumb, mute, silentunable to speak because of hereditary deafness