Sindar, Dwarves, and Glass
 

In The Silmarillion it states:At first I was confused, "Why would the Elves steal a word from the Dwarves?" Then I read up on the Sindar, and learnt that the Sindar and the Dwarves were friends.

So then I wondered, "Wouldn't they already have a word for glass?" Then the idea hit me: Do you think it's possible that the Dwarves taught the Sindar how to make glass, and so that's the reason they took the word?

What light through yonder window breaks? It is the forge lamp...
 

That is the obvious answer that comes to mind.

That could very well be the case.

The Sindar were a rustic people compared to the Noldor. I would suspect their crafts to be less advance than that of the dwarves.

or...
 

Excellent deduction. Another possibility is that Aule and Co. had glass in Valinor and that the word, via Valinorean via Aule's teaching the Dwarves got glass making and the name there. Or Melian recalled the [hypothetically Valinorean] from her time in the Undying Lands...

I think if that were the case then it would have been cited as such.

"Yet another example of the mystically magical wonderfulness of Melian the Maia."

I personally should consider it likely, if not certain, that the Dwarves introduced the Sindar to glass. After all, they also introduced them to chainmail, and seem to have been the first ones to make them swords (Telchar, a Dwarf of this era, is known to have been the maker of Narsil, which I think we can guess came to the House of Andunie via inheritance from the First Age).

However, it was not a one-way street. The Sindar and the Dwarves did a great deal of commerce in these early years, to their mutual profit (seeing the Silmarillion, the accounts of the building of Menegroth). Surely there would have been more than just an exchange of products. As the chainmail shows, there would also have been an exchange of ideas. It is entirely possible therefore, although not necessaily conclusive, that the Dwarves invented glass, or introduced it to the Sindar.