Same word as quiet:
buttoned up, clammed up, close, close-mouthed, could hear a pin drop, dumb, hushed, hushful, inaudible, low, low-pitched, muffled, mute, muted, noiseless, not saying boo, peaceful, quiescent, quieted, reserved, reticent, secretive, silent, soft, soundless, speechless, still, stilled, taciturn, tight-lipped, uncommunicative, unexpressed, unspeaking, unuttered, whist
buttoned up, clammed up, close, close-mouthed, could hear a pin drop, dumb, hushed, hushful, inaudible, low, low-pitched, muffled, mute, muted, noiseless, not saying boo, peaceful, quiescent, quieted, reserved, reticent, secretive, silent, soft, soundless, speechless, still, stilled, taciturn, tight-lipped, uncommunicative, unexpressed, unspeaking, unuttered, whist