| clandestine |
| classified |
| closed(adjective, calm, quiet, smooth, tranquil) |
| cold(quiet, gentle, aloof, reserved, reticent) |
| collected(quiet, gentle, aloof, peaceful, reserved) |
| confidential |
| cool(adjective, quiet, gentle, aloof, reserved) |
| could hear a pin drop(expression, adjective, idiom, close, quiet) |
| curt(aloof, reserved, reticent, taciturn, uncommunicative) |
| deathlike(adjective, calm, quiet, smooth, tranquil) |
| deathly(adjective, calm, quiet, smooth, tranquil) |
| deathly quiet(expression, adjective, calm, quiet, smooth) |
| deathly still(expression, adjective, calm, quiet, smooth) |
| demure(adjective, quiet, gentle, aloof, peaceful) |
| discreet(adjective, quiet, soft, low, restrained) |
| dour(aloof, reserved, reticent, uncommunicative) |
| dried-up(aloof, reserved, reticent, uncommunicative) |
| dumb(adjective, close, quiet, soft, low) |
| enigmatic(mysterious, private, reticent, taciturn, uncommunicative) |
| feline(mysterious, private, reticent, taciturn, uncommunicative) |