Yes, I know, it's the plural form of Sun, but the word Sun likely predates our understanding that stars and our Sun are the same thing.

I get "stars", but where did "suns" come from?

Probably the same place 'realities' or 'universes' came from. Nouns have plurals even if the actual plurality makes no sense

My take is that the word "suns" would imply someone else's Sun in various systems. I don't think it would be correct to call a star a sun if it didn't have planets and occupants (past or future).

Since "the" is needed, "the Sun" is more of a generic placeholder, whereas Sol is its actual name in English. So you could be on a different planet somewhere and refer to its star as the Sun (implied of this system), or its name.

It's also quite possible "suns" has been used in the past for all stars, this is just my take given how the words tend to be used by us.

historically many early humans thought the sun was a different sun every day.

Yeah, I think like this too. Considering systems can have multiple stars which have planets with varying orbital planes because of this.

Imagine the Solar System has some small red dwarf called Sol B out past Saturn. Neptune and Uranus orbit it as the star orbits Sol. Then waaay out further is Sol C, which orbits Sol too, but it's alone and not at all dense.

Sol, Sol B, Sol C are all stars in the Solar System. Sol and Sol B are suns, Sol C is not.

While that does follow modern naming convention for multiple star systems, the primary star is denoted with an A. Since we already call it Sol, we'd probably make an exception in this case and come up with a stellar name for the other stars found rather than use the B. But your point stands, a star without a planet doesn't seem to be a "sun".

Tatooine maybe?

[…] but the word Sun likely predates our understanding that stars and our Sun are the same thing.

And, does its plural so as well?

In the morning I greet a bleary, foggy eyed sun. At noon, I see a cruel and imposing sun. In the evening I see a sun, red and weeping into the sea. At night, where have my suns gone?

In what context did you hear the word "suns"? Presumably, it had to be invented for whatever context required the plural of sun. In Star Wars, Tatooine has two suns. In the galaxy, there are many suns. It's not like it took much thinking to figure out how to pluralize sun.

Also, in ancient times I think "suns" was another way to say "days"

I think they were using phrases like "burn you with the heat of a thousand suns!" Long before they realized there actually were more suns out there.

Humans using words for things that don't necessarily really exist is something new for you? Like... You've never heard about the concept of "stories"?

The year was 1968. The National Basketball Association was expanding and two cities were selected. One choice would go to Milwaukee and that team would choose the Buck as its symbol) nickname. The other choice would be Phoenix, in the Valley of the Sun and need to be the first representation of professional sports in the entire state of Arizona. As the Sun was so important to the identity of Phoenix, they would also be the Sun. But what would the group be if each player was a Sun?

On that note, I have heard the term "many moons" to describe the passage of time, one could use suns in the same way.

OK alien overlord.

Is this from something? Its very well written.

Well, you see...

Thanks! Nope, I made it up. But, I'm certain that I borrowed the motif of many Suns from some poetry I've read.

probably happened shortly after language happened