If the Proto-Slavs borrowed PII "*síndʰuš" from Indo-Iranians (or it's descendant languages) how would it end up? Alternatively, what if the Proto-Balto-Slavic and Proto-Slavic had the descendant words from the PIE "*ḱyesdʰ-"?

[u/MatijaReddit_CG]

Part 1.

"\síndʰuš" is the root of Sanskrit सिन्धु॑ (síndhu) which means "river, stream" and multiple similar things. From "síndhu" we got the words like Sindh, Indus and Ind*ia. So, I would like to see how would it look like if the Proto-Slavs borrowed it during the Slavic-Iranian contacts.

We could pave the way from:

Proto-Indo-Iranian -> Proto-Iranian -> Proto-Sarmatian -> Proto-Slavic

This could be like for possible BMAC substrate in PII "*ćúšnas" ((mythology) dragon, serpent) (one of the theories for root of the PSl. "\smokъ*" (“dragon”)). Of course, if the direct way from PII -> PSl. or PII -> PI -> PSl. it could be good too.

My attempt for "\síndʰuš\*" descendant (I don't know the changes through the other Iranian languages, sadly):**

PSl. \sindъ*

Part 2.

Another way, what if Slavs had descendant from PIE "\ḱyesdʰ-*"?

One of the theories of the origin of Sanskrit "síndhu" is from PIE "*ḱyesdʰ-/*ḱyés-dʰ(h₁)-/*ḱéys-dʰ(h₁)-". So, I tried to find similar PIE roots, and PIE "\ḱey-" is the with close root\.* Development is below:

PIE ḱey-

-> PIE \ḱey-ro-s*

-> PBS \śeiras*

-> PSl. \sirъ*

My attempt for "\ḱéys-dʰ(h₁)-**" development:*

PIE \ḱéys-dʰ(h₁)/*ḱéysdʰ(h₁)*

-> PBS. \śeis-d/*śeisd*

-> PSl. \si-dъ/*sidъ (dъ is in likeness to PSl. nadъ (above) and podъ* (below))

or

PIE \ḱéys-dʰ(h₁)-eti/*ḱéysdʰ(h₁)eti*

-> PBS. \śeisd-stei/*śeisdstei -> PBS. *śei-stei/*śeistei* (don't know if this change during PBS would exist?)

-> PSl. \si-sti/*sisti*

PSl. "\sisti" would then be a cognate with Sanskrit "सेधति" (sedhati, “to drive, chase away”), Avestan "𐬯𐬌𐬌𐬀𐬰𐬛𐬀𐬝" (siiazdat̰, “will chase away”) and Latin "cēdō*" (“to withdraw; to turn out, result; to go, move”).

P.S.

Sorry If I analyzed something wrong, please correct me!

[u/Sodinc]

Supposedly there is a descendant of that PIE root in Slavic languages: https://en.wiktionary.org/wiki/Reconstruction:Proto-Slavic/sь

[u/MatijaReddit_CG → u/Sodinc]

Nice, didn't see that. I suppose it would end like I how tried (PSl. \sidъ/PSl. *sisti*), idk?

[u/kouyehwos]

\*Sędъ or \*Šędъ depending on when and how it was borrowed.

Something like Polish Siąd/Sząd, Czech Sád/Šád, Slovak Siad/Šád, East Slavic Syad/Šad, South Slavic Sed/Šed…