| incomprehensible |
| indistinguishable |
| insensible |
| mousy(still, hushed, soundless) |
| mumbled(adjective, quiet, soft, low, unclear) |
| obscure(adjective, quiet, weak, pale, unclear) |
| quiescent(adjective, close, quiet, soft, low) |
| slight(adjective, weak, pale, subtle, imperceptible) |
| stifled(adjective, dull, quiet, weak, soft) |
| unuttered(adjective, close, quiet, soft, low) |
| whist(adjective, close, quiet, soft, low) |
| wordless(adjective, quiet, soft, low, still) |
| bated(adjective, dull, weak, soft, gentle) |
| blurred(adjective, weak, pale, unclear, hazy) |
| buttoned up(expression, adjective, close, quiet, soft) |
| clammed up(expression, adjective, close, quiet, soft) |
| close(adjective, quiet, soft, low, still) |
| close-mouthed(adjective, close, quiet, soft, low) |
| closemouthed(adjective, quiet, soft, low, still) |
| could hear a pin drop(expression, adjective, idiom, close, quiet) |