Aether is supposed to be the material that the heavens is made up of, separate and distinct from the base, worldly elements. If you really want to translate it from classic greek elements to D&D cosmology, aether would be the substances the Astral and the Outer Planes are made up of, which is distinct, separate and opposite of the Inner Planes.
A second option for translating aether to D&D would be "arcane" spells such as magic missile - spells made up of "magic force." Though I personally would associate it with Earth than its own element or state of matter, I find that I'm in the minority when it comes to pop culture's take on the matter.
Also, of note is that poison spray is now a necromantic cantrip, which seems to me to suggest that elemental poison is going to be associated with the negative plane (/shadowfell in my suggested cosmology).
Yeah. Ether [αιθηρ] is originally the "upper atmosphere" high above the clouds. By contrast, the Air [αηρ] is the "lower atmosphere" below and including the clouds, and can translate literally as "haze".
As Hellenism (the mixture of Greek and nearby cultures, especially Egypt and Babylonian) began to explore elemental units of matter, eventually the Four Elements of matter emerge − Fire, Air, Water, and Earth. Then the Ether functioned as the Fifth Element, as the "eternal" element beyond these four temporal elements. Traditions about what Ether is differ drastically, including the concepts of spirit, soul, energy, and space. In all of these traditions of Ether, the Four Elements are understood to emerge from the Fifth and to interact with each other within it.
By the Medieval Period, such as during the 1100s, a surprisingly modern explanation for Ether also emerged among the other explanations. Here, Ether was understood to have properties of both Fire and Water, and yet to be neither, reminiscent of particle-waves. Even more significantly, Ether was identified as a "force" that is invisible, yet physical and while strictly lacking matter is able to keep the celestial objects in orbit. In other words: Ether is gravity. In this same view about Ether as force, the Four Elements were understood to be states of matter: solid, liquid, gas, plus plasma being "the fire of the heavens" or "the fire that burns fire". The sun, stars, and lightning were understood to be made out of the Heavenly Fire, which is nonidentical with ordinary flames. These states of matter arent particles in themselves, but rather the "forms" that any kind of particles of matter might take. Ordinary water can become Earthy ice, Watery water, and Airy steam, and likewise metals like gold and mercury can. The Four Elements are states of matter.
In a D&D context, the Fifth Element of Ether already exists as the stuff of the Ethereal Plane. It is Force.
Meanwhile the D&D "soul" is a microcosm of every plane in the multiverse. It includes the physical body of animal life, being made out of matter, as well as the spirit of a person that can exert influence ethereally, telekinetically, such as disembodied ghosts do, and also encompasses the mindscapes of the thought stuff of the Aster of the Outer Planes including the Astral Plane.
Meanwhile all Force damage, Force effects such as telekinesis, and Force constructs that are physically quasimaterial but actually immaterial, are all made out of Ether, the same stuff that gravity is made out of. Using gravity-like Force to squeeze someones heart or choke someone or cause brain aneurysms, are normal examples of what Force damage is. Note, because a Force
construct simulates the shapes of matter, it can also deal Weapon damage: Bludgeon, Pierce, and Slash.
In the context of the
Poison Spray cantrip, to classify it as Necromantic requires clarification. I suspect what they are trying to convey is using Poison damage as a way to express damage from a "disease", in the sense of anti-life and rot. If Poison can mean "disease" as well as "toxin", then the description of Poison damage in the Glossary in the 2024 Players Handbook needs to make this clear. It makes enough sense for Necromantic to include disease tropes. Consider how much of the gothic horror vampire imagery comes from the symptoms of "consumption", tuberculosis.
