Etymological reason behind Lao's many seeming variants for "stairs"?

Question

I'm in Laos studying Lao on my own and came across the fact that different sources have slightly different words for "stairs" and the SEAlang Lao dictionary has even more:

• ກະໃດ - 15 Google results
• ກະໄດ - 7,400 Google results
• ຂັ້ນໃດ - 36 Google results, in an old Lao to English phrasebook found on my guesthouse bookshelf
• ຂັ້ນໄດ - 75 Google results, in current Lonely Planet Lao Phrasebook
• ຄັນໃດ - 8 Google results
• ບັນໄດ - 50 Google results

Except for the last one, they all seem like they could plausibly share an etymology as a borrowing from a language with different phonology.

For the second syllable / morpheme the two variants ໃດ dài and ໄດ dài have the same vowel quality, length, and tone. Lao shares with Thai the quirk of having two letters for the same /ai/ vowel sound.

For the first syllable / morpheme there are three possibilities, all beginning with a velar stop and with a short /a/ vowel: ກະ ká, ຂັ້ນ kʰȁn, ຄັນ kʰán.

But there are both voiced velars and unvoiced unaspirated velars and in the latter case both the high class and low class consonant letters may be used.

Also the syllable / morpheme may or may not end in a nasal. Either way it will be a "live" syllable as far as tone rules.

The resulting tones of both syllables end up having multiple possibilities as well.

กระได (kraˈday) and บันได (banˈday) seem to be the only possible Thai cognates. The second uses a first syllable / morpheme compatible with our last Lao word, which is not similar to the others so we didn't analyse further. But the first does seem sufficiently similar to all our other Lao words. Could they all be related? From whence do they originate?

Answer 1

My best guess is that the final syllable is from the Khmer word for to walk. It makes sense based on how the Khmer word for stairs is spelled. At least I cannot find any other good explanation as I do not know where the Thai syllable ได should come from besides Khmer.

ដើរ /daə/ to walk, to go, to move, to operate; to be working, to be operating (e.g. machinery).

ជណ្ដើរ /cʊəndaə/ ladder, stairs, staircase

I am not sure about the first syllable of the Khmer word for ladder, but it might be from: ជាន់ /coan/ floor, story, level, stage, class, status

This might also explain why the final syllable is sometimes written ໃ and not ໄ since if ໃ was previously pronounced differently, it might better reflect the Khmer vowel aə which is not present in Thai/Lao.

Answer 2

There’s no reason to assume this is a borrowed word, although Tai languages have borrowed some words with this shape (minor syllable – major syllable, or “sesquisyllabic”) from Khmer and Mon. Marvin Brown in “From Ancient Thai to Modern Dialects” includes several words with the กระ- minor syllable on his list of common Tai etymons, such as กระดูก /kradu:k/ “bone”. While he doesn’t list กระได among them, numerous cognates in other Tai languages suggest that if this word is borrowed, it happened very early. Some of these cognates: Thai northern dialect /khan dai/, Tai Lue /xɨn dai/, Tai Dam /lai/, Northern Zhuang lae /lai24/.

Why the variation? It may be that the standardization process in Lao has not progressed to the extent it has in Thai. But more generally, it’s likely that the iambic stress pattern of words like this means that the minor syllable is less stable than the major one.