Similar word to silent:

bashful, buttoned up, checked, clammed up, close, closed up, closemouthed, curbed, dumb, dummied up, faint, hush, hushed, iced, inarticulate, incoherent, inconversable, indistinct, inhibited, laconic, mousy, mum, mute, muted, noiseless, nonvocal, not talkative, reserved, restrained, reticent, shy, silentious, soundless, still, struck dumb, taciturn, tongue-tied, unclear, uncommunicative, unheard, unsociable, unspeaking, voiceless, wordless, zipped