quiet
謐 centers on quietness, especially a calm, peaceful silence or stillness.
謐 combines 言 (speech, words) with a phonetic component historically related to 必 over 皿. The exact historical development is uncertain, but the character likely expressed quietness through the idea of restrained speech.
Words (言) are stilled when a calm heart (心) rests under a lid (皿), creating a quiet, peaceful silence.
For ヒツ, imagine a quiet room where the only sound is a soft hiss: hiss -> ヒツ, and the silence is so deep you can hear it.
peace (esp. of the world); peace and calm; tranquility; tranquillity