Om mani padme hum: an etymology of a mantra common to Hinduism and Buddhism

I was watching the TV this morning and heard some oriental-looking people in a (apparently) Tibetan film saying a sentence I had heard already in other films about India and the Tibet: oṃ maṇi padme hūṃ (Devanagari ॐ मणि पद्मे हूँ), probably the most famous mantra in Buddhism, the six syllabled mantra of the bodhisattva of compassion, Avalokiteshvara (Tibetan Chenrezig). Then I remember that my sister-in-law has Oṃ (Skr. Aum) tattooed on his hand, withoug knowing what that means, and after finding a website that asserts “mani” is from Tamil origin (‘exported’ to Latin), I decided to write this (incomplete) post about its known etymology.

After the Wikipedia article:

Mantras may be interpreted by practitioners in many ways, or even as mere sequences of sound whose effects lie beyond strict meaning.

AumOṃ: Aum (also Om, Devanagari , see picture) is a mystical or sacred syllable in the Dharmic religions, consisting of the three sounds (a), (u), and (m), representing various fundamental triads and believed to be the spoken essence of the universe. It is placed at the beginning of most Hindu texts as a sacred exclamation to be uttered at the beginning and end of a reading of the Vedas or previously to any prayer or mantra. The Mandukya Upanishad is entirely devoted to the explanation of the syllable.With preceding a or ā, the o of om in Sanskrit grammar in sandhi (Sanskrit: संधि, “joining”) does not form vriddhi (au) but guna (o) per Pāṇini 6.1.95.
The Sanskrit name for the syllable is praṇava, from a root nu “to shout, sound, praise”, verbal pra-nu- being attested as “to make a humming or droning sound” in the Brahmanas, and taking the specific meaning of “to utter the syllable om” in the Chandogya Upanishad and the Shrauta Sutras.
In Puranic Hinduism, Aum is the mystic name for the Hindu Trimurti, and represents the union of the three gods, viz. a for Brahma, u for Vishnu and m for Mahadev which is another name of Shiva. The three sounds also symbolise the three Vedas (Rigveda, Samaveda, Yajurveda).

Maṇi-:“Jewel, gem, cintamani”. Compare Avestan maini, Latin monile (hence PIE *moni-?), borrowed into Tamil mani.

Padma: “Lotus”. I couldn’t find any known relatives. Someone out there?

The middle part of the mantra, maṇi padme, is often interpreted as “jewel in the lotus” Sanskrit maṇí “jewel, gem, cintamani” and the locative of padma “lotus”, but some interpret Maṇipadme as a vocative, not a locative, addressing a bodhisattva called Maṇipadma, “Jewel-Lotus”.

Hūṃ: is an exclamation or interjection, the like of which are also frequently found in mantras and in old Hittite texts.