Happy "Friday Word List" from al-Tha‘alabi's Fiqh al-lugha wa-asrār al-‘arabīya (Fundamentals of Language and the Secrets of Arabic).
Types of Barely Perceptible Sounds
Among the almost imperceptible sounds are al-rizz (a sharp rumbling of the belly), then al-rikz (a slight, far-off cry, such as the voice of hunter calling his dogs), which is mentioned in the Qur’an: And how many generations before them have We destroyed! Can you (Muhammad) see any one of them? Can you hear from them the slightest of sounds? (Surat Maryam: 98).
Then there is al-hatmala (to murmur to oneself) which is softer than the tones made when whispering into someone's ear. Then there is al-haynama (to mumble-read), which is like reading aloud, only unclearly so. As the poet Al-Kumayt ibn Zayd al-Asadi put it: Whenever I’ve witnessed foolish speech, it was spoken by men who murmured and mumbled.
Then there is al-dandana, which is when a person speaks and you can discern its prosody but understand nothing of the words because that person is hiding them from you. This appears in the hadīth: As for your mumblings and those of Mu‘ādh, we understand them not.
Then, al-naghm, which is the ringing of speech and the beauty of its sound. Then there is al-nab’a, which is a soft sound. Finally, there is al-na’ma (to sigh or moan), which is a very slight sound.
— Fiqh al-lugha wa-asrār al-‘arabīya, ed. Yāsīn al-Ayūbī (Saydā’: al-Maktaba al-‘Usrīya, 2008), p. 237.