They have “ray of frost”. They can understand “radiation”. Not necessarily what is radiating but the word itself is old.

radiation(n.)

mid-15c., radiacion, “act or process of emitting light,” from Latin radiationem (nominative radiatio) “a shining, radiation,” noun of action from past-participle stem of radiare “to beam, shine, gleam; make beaming,” from radius “beam of light; spoke of a wheel” (see radius).

Tldr “radiate” is like 1500’s whereas “emitter” is a fairly modern word, from the 1880’s.

The latin source word is much older than 1500s, but the question is whether they understand what it’s about.

Both the 15th century “radiacion” and the latin “radiationem” are about emitting light and are synonymous with “to shine” or “to glow” (though without the heat connotation).

None of that conveys the sense of danger and fear of death that the modern word “radiation” means.

Kinda like how the word “plane” was in use in English in the 1600s and derives from the much older Latin word “planum”, but if I’d tell some from 1600s England or from ancient Rome that I took a plane/planum to another country, they’d be utterly confused about what that means.

The word is the same (or at least very similar), but the concept is unknown.

So you need to find a concept that’s similar to what you want to convey, and then use the fitting word.

For example, someone from the 1600s might understand the term “flying machine” (which was a well-known word in use in research and “science fiction” at that time).

This glyph clearly portrays the object with the ️ symbol bringing someone back from the dead! We should consume the blue powder inside this metal case, as it’s clearly a kind of medicine

This kind of symbology is never going to work. We know what archaeologists do when they understand the “you will die if you break this seal” message. Ain’t no symbol is going to keep a damn human from cracking open the glowy blue box

I mean, testing showed it generally got the point across even if people didn’t understand why it was dangerous

I’m curious what testing and what people. Unless it’s an as-yet uncontacted tribe in the Amazon rainforest, I’m not convinced that they successfully made a universally understood sign of danger.

And even if the message gets across, I will reiterate: when archaeologists understand that a message says “entering here will kill you,” it only makes them want to enter more. Future post-post-apocalypse archaeologists will treat our nuclear waste disposal sites with as much care as a 19th century British scholar would have treated the pyramids. We’re a curious bunch. Best we can hope for is that we keep making Geiger counters

Long-term nuclear waste warning messages - Wikipedia

(en.wikipedia.org)

People have put alot of thought into this exact topic and there’s no easy answers

I’m not feeling creative today so I’ll just write “Dildo joke”.

No, they don’t convey the sense of danger, I agree.

But “light-emitter” would be worse than “it radiates death/evil”, imho

“Something something - anything if you’re brave enough”

I’m well aware. Personally, I like to think of it from the opposite perspective; what message might we find that someone could have written 10,000 years ago that would convince us not to mess with something? The only proposals that work are ones that involve translating the dangers of radioactivity to new languages. Either that, or bury it deep in a place that isn’t expected to be particularly habitable for a few thousand years. Every physical marker is just begging for an archaeologist to discover why exactly they were constructed