"et" is usually a suffix for feminine beings things (ie "Sekhmet", "the female powerful one" ["powerful one" is just "Sekhem"], "Kauket", "dark female one" ["dark one" is just "Kek"])
The feminine of Amon is technically Amaunet, but it could be spelled as "Amonkhet" especially since there are no preserved vowels.
There's definitely some wiggle room with the vowels, but that wouldn't explain where the -kh- comes from if 'Amonkhet' was supposed to be the same word as 'Amaunet'. Even with different conventions of transcription that exist for ancient Egyptian (e.g. between different modern day languages like English and German), I'm pretty sure the consonant cluster would be preserved as either -kh- or -ch- and was probably spelled out in hieroglyphs as well. So I don't think you could just spell 'Amaunet' with an optional -kh- in there. I'm not an egyptologist or anything, though, just talking from my own experience. So the bottom line is, I still think 'khet' probably has a meaning of its own rather than just making the word feminine.
Amon/Amun is also one of main deities of ancient Egypt, worshiped nearly to the point of monotheism for several centuries as Amun-Ra. It's safe to say that the name is pretty big for evoking "Egypt!"
And that's exactly what I thought when I first read the name in the announcement. But I would be sorely disappointed if they just made up the name that way and it turned out to be gibberish, and given the naming conventions of many other planes, it makes sense to look for a possible meaning behind the name of a new plane. The Egyptian words and syllables that people are most familliar with come from names of pharaohs and gods, and that's a good starting point for coming up with a meaningful plane name, because the names of Egyptian gods and paharohs pretty much always mean something. From a creative perspective, it would be too good an opportunity to achieve both resonance and meaning to just string meaningless sounds together that have nothing to do with the plane itself. As we have all demonstated now, many people are familliar with the name of Amun/Amon, and Wikipedia cites a credible source for it meaning 'hidden' or 'invisible' (I also checked the Wikipedia article in a few other languages that I can read well enough to tell they give the same meaning). Being 'hidden' or 'invisible' is a quality we know planes in Magic can have, so I really want to believe I'm on to something there. It's just too good to be coincidence.
Maybe I'm in the minority here, but I think it's weird that people keep trying to make up reasons why Amonkhet could be the place Vraska went to when it's pretty clear that she's going to whatever dark void she ended up in when she first planeswalked. That place wasn't an Egyptian plane with crazy Bolas motifs. It was a black nowhere that was nothing in all directions. Whatever it is, it is probably her safe space that she retreats to so she can collect herself and plot, sort of like a certain meditation realm, but more naturally occurring. Why Project Lightning Bug can't identify it is anyone's guess, especially since we just found out that was a thing the project could even do.
That 'confirms' nothing.
Nor does Kamigawa have anything to do with rivers, for example.
It's a stretch to say it's hidden or invisible.
Kamigawa doesn't have anything to do with rivers (at least not literally), but it has
a lot to do with kami. Sure, I'm stretching the definition of 'confirm' quite a bit, but I think it would be pretty odd if the recent info about Vraska 'walking to an invisible destination shortly after the announcement of a plane that has a word for 'invisible' in its name were completely unrelated. We already learned that Vraska is up to something sinister a few weeks before that, so why would we need that second piece of info if it wasn't somehow important for the transition to the next block (assuming she won't randomly be involved in
Aether Revolt)? The only other way in which I could see that making sense would be if Ravnica III was the next block after
Hour of Devastation and all of this was a hook laid out two blocks ahead. I mean, that's not any more speculative than assuming she planeswalked back to that black, empty void. We just don't know much about that place, but I don't think it would be particularly useful to Vraska, except for resting and hiding from planeswalkers temporarily. Is there any info about that black void other than
The Shadows of Prahv, Part 2? Because all it says there is this:
"Just before your 'guard' would have killed me, I was torn from this world. I was cast into a dark tomb with no way out." [...] "It felt like lifetimes before I learned how to escape, to slip the confines of a world. But during the eternity I was trapped, I resolved that all should receive the death they deserve." Heck, I'm not even sure this describes a definite place rather than just being thrown into the Blind Eternities and then being stuck on a random, unspecified plane due to not knowing how planeswalking works. I know it might just be many people's wishful thinking, but establishing Vraska as an agent of Bolas would make sense to me, and then she would have a reason to planeswalk to Amonkhet. With Ajani suddenly showing up, Tezzeret making a comeback and every 'walker conveniently knowing everyone else, it looks like this is heading in an anti-Bolas direction where 'walkers will either side with Bolas or the Gatewatch in the not-so-long run. And surely Bolas would take measures to hide Amonkhet and prevent random planeswalkers from stumbling in and ruining things in his absence. If he's been there for more than 1,280 years, it might have been intended to keep out Ugin specifically.