In scripture, aionios’ use to modify both judgment and the fire that destroyed Sodom was enough to indicate to me that aionios does not always, if ever, mean “endless”. I trust that Judgment does not go on and on and on, but that it is a “day” or set period of time of judgment, not something that goes on forever. And the fire that destroyed Sodom was certainly not something that lasted forever, was endless. As others have noted, it’s a word that connotes quality, not necessarily quantity. So the aionian judgment that scripture speaks of is not “endless” or “everlasting” judgment, but it is judgment that is from God. And the fire that destroyed Sodom was not endless or everlasting fire, but it was fire that came from God that was related to the judgment of God.
And then there is the fact that in the LXX it was used to translate the concept of Olam Haba, the age to come, even the Messianic age to come. Olam haba is a pictoral word which speaks of that which is over the horizon, vague, distant, not distiquishable, and somewhat just out of site. It also speaks metaphorically of that which is beyond our understanding, something we cannot fully grasp.
But if a person’s belief in ECT rests on aionios ONLY meaning “endless” or “everlasting” then no evidence to the contrary will persuade them otherwise. Hell, ECT is a foundational element of the traditional bad-news, and if that is shaken it shakes with a level 9.0 earthquake the world-view based on the assumption of the damnation of others!
To me aionios is really a minor issue because the fact that Hell is not named or warned of clearly in the Law and the prophets was huge. Something so important as Hell would be all over scripture, like it is in the mistranslated KJV. Of course, any student of Hebrew and Greek can quickly affirm that neither Sheol, Hades, or Gehenna mean Hell/ECT. The wages of sin is “death”, not ECT.
And btw, it never ceases to amaze me that people have such faith in Jesus for the damnation of others, faith that Jesus fails to save untold millions of people - “others” of course. It’s much more difficult to have faith in Christ for personal salvation if salvation is limited to only a select few or only the qualified few. If however Christ saves everyone, then I trust He can even save me, the chiefest of sinners.
When did “eternal” change from “ethereal” to “endless”? I don’t know that it has wholly changed. In some literary contexts “eternal” is still meant to convey the meaning of “ethereal” or that which is beyond the constraints of time as opposed to that which is “endless”. Eternal - that which is “out there”, beyond what we can see/understand completely.