1. (a.) Not capable of being sounded or fathomed; unfathomable.

2. (a.) Having no sound; noiseless; silent.

abysmal abyssal bottomless cavernous deep as hell echoless fathomless gaping hush hush as death hushed inaudible mousy noiseless plumbless plunging quiescent quiet silent still still as death stilly subaudible unarticulated unfathomable unfathomed unhearable unpronounced unsounded unuttered unvocalized unvoiced whist without bottom yawning