Also, I guess - Urdu, Arabic, Farsi, Pashto, Mongolian - are different languages, and all of them would have been prominently used in India at some time by the invaders; so this is what that also needs to be in mind while looking for the
words starting with the sound of 'S' that are not of Indian origin, but of-whom We are aware of; that to which language do they actually belong and when is their earliest recorded use in that particular language !! Hang-on, before proceeding, read the whole post. I am not 100% sure but Upender Singh Laakda's views also needs to considered by the present day Scholars !!
Also, we have seen in the past that lots of words from different languages got introduced in-between different languages over time; there are many examples of this !! For example: "Persian has had a considerable influence (mainly in the lexicon) on neighboring languages, particularly the Turkic languages in Central Asia, Caucasus, and Anatolia, neighboring Iranian languages, as well as Armenian, and Indo-Aryan languages, especially Urdu. It has exerted less influence on Arabic, while borrowing much vocabulary from it.... With a long history of literature in the form of Middle Persian before Islam, Persian was the first language in Muslim civilization to break through Arabic’s monopoly on writing, and the writing of poetry in Persian was established as a court tradition in many eastern courts." (Source: Persian language - Wikipedia) Can anyone deny any chances of the words being assimilated in-between these different languages over time !!
Also, I suppose no single language with a unique / specific / single accent is spoken by all the residents in any country on Earth (at any period of time !!), guess so; this is also important that who was on front at the field !! I will take example of Persia, like they have spoken Pehlevi, Farsi (Parsi / Parsee ?!), etc. during ancient time. Please note that 'F' and 'P' are interchanged there (and such a change in that one single country !!), interesting, isn't it !!
When they were at the borders of Sindh, how many of them were speakers of Pehlevi and how many of Farsi, please mind that they will be called as Farsis (people) or Persians anyways, even if they were using Pehlevi or Farsi (another name for Parsi (language) / Parsee (language) / Persian (language) I guess !!) or any other language that was also spoken over there; so how many languages were used by the people of that region, and with what accent, this is important to know !!
Also, did the invaders not spelt Sindh as Hind, and Sindhu river as Hindu river ?! Also, the languages used at different times are different like - Urdu, Arabic, Farsi, Pashto, etc. If Sindh was spelt as Hind at-least for once (due to linguistic differences though), then I am satisfied with Upender Singh Laakda's views !!
Linguistic differences are important, for example: "Some sources report that it was Alexander the Great who first renamed the River Sindhu as the Indu, dropping the beginning “S”, thus making it easier for the Greeks to pronounce. This became known as the Indus. His Macedonian forces thereafter called the land east of the Indus as India, a name used especially during the British regime. Before this, the Vedic name for the area was "Bharath Varsha", which many people still prefer to call by this name." (Source: SikhiWiki)
See what a linguistic issue can come-up with !!
Maybe, Sindh was in-reality spelt as Hind, but later-on a bad meaning was intentionally imposed on the word, because they could not think of something else but the first word with which the geography and people over there were identified (maybe, this word was the best possible choice actually for them to target; who may or may not be Persian invaders, could be Arab invaders, Mughal invaders, Pathan invaders, Turk invaders, etc., could be anyone of them; so it may not be justified to claim that any Persian would have done this !!); and the real thing maybe is that Hindu is merely a translation (or a synonym in this case) of Sindhu !!
Please be aware of the example that I have pointed-out above, where 'F' and 'P' are interchanged, due to linguistic issues !!
Furthermore, there are also chances that Sumerians might have mispronounced the word 'Sindhu' !!
Also:
"Hiuen Tsang who visited this country between AD 630 and 645 says that while the word “Shin-tu” (Chine-se for “Hindu”) could be heard outside our borders, it was unknown within the country." ( Source:
http://voiceofdharma.org/books/htemples2/app3.htm )