| soundless(adjective, close, quiet, smooth, soft) |
| speechless(adjective, close, quiet, soft, low) |
| stable(adjective, calm, quiet, smooth, tranquil) |
| stagnant(adjective, calm, quiet, smooth, tranquil) |
| static(adjective, calm, quiet, smooth, tranquil) |
| stationary(adjective, calm, quiet, smooth, tranquil) |
| still(adjective, calm, close, quiet, soft) |
| stilled(adjective, close, quiet, soft, low) |
| stock-still(adjective, calm, quiet, smooth, tranquil) |
| struck dumb(expression, adjective, close, quiet, restrained) |
| surreptitious |
| tended(adjective, secure, safe, snug, intact) |
| tongue-tied(quiet, still, shy, reticent, silent) |
| tranquil(adjective, calm, quiet, smooth, silent) |
| unassailable(adjective, secure, safe, snug, intact) |
| unclear(still, hushed, soundless) |
| undamaged(adjective, secure, safe, snug, intact) |
| under lock and key(expression, adjective, idiom, secure, safe) |
| undercover(mysterious, private, reticent, taciturn, covert) |
| underhand |