So now, back to the discussion.
What ancient indian asked was why after many searches he wasn't able to find the cousins of the word "aum" in other Indo-Iranian(ii) &/or Indo-Euro(ie) languages.
To be able to locate such cognates you need to know phonological change rules (or patterns, if you will)
Basically sound pattern changes in languages, usually follow certain rules. I don't know much, since I'm not a trained linguist.
Look it up, this may help you widen the search for cognates of the word "aum"
I haven't gone through the various possible cognates or origins of aum, there might be in other Indo-Iranian (or even Indo-euro) languages.
@Peter has posted some posiiblities from wiki.
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Now another possiblity is in the first quote of mine (emboldened and underlined)
When people come in contact there is exchange of tools or techonolgy or ideas or practices or vocabulary/lexicon.
This might be the origin of many words like "aum". Do remember that Indo-Aryan languages have come in contact with at least Austroasiatic and dravidian languages in the Indian-subcontinent. Hence there might have been exchanges.
For eg: You cannot find the origin of the word "mango" in IE languages but that doesn't mean English isn't IE language.
Mango comes from Tamil "mangai". So does Catamaran (katta maram).
Similarly "business mogul": Mogul comes from Hindi/Urdu "Mughal" ultimately meaning Mongol.
More examples "Bahadur", "Jackfruit", "rice" so on.
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