Thank you, Ed for starting this thread. It has been fun watching, in a cynical bemused kind of way, the way the thread has evolved. It is great when we can disagree without being disagreeable.
In my field of endeavor, someone in a position of authority defines a word in a certain way and then, for purposes of discussion, that definition is what is used, no matter how stupid or unrealistic the word might seem to someone outside the field. That way, whenever the word is used, everyone in the field knows exactly what it means.
I was shocked a few years ago, when, on this forum, someone disagreed with how the word "scale" was to be used. After 30+ years of reading "S Gaugian"and the NASG Dispatch, I was shocked that there was anyone actively modeling in S who didn't use the word in the same way that it was used in those publications. I guess I should get out more.
As to the word "Hi Rail" I believe I first saw the word in a book from the 1940's called "Riding the Hi Rail Route" or something like that. It told the story of a man and his sons who tried to build a realistic railroad in the early post WW II period, but because of the prohibitive cost of "Scale" O gauge locomotives, he chose to use Lionel trains and track, but he detailed and painted the engines and rolling stock to look less toy like, built "scale" rolling stock from kits and put Lionel trucks on them, and built what was at the time realistic scenery (which consisted of cardstock buildings, landforms made of plaster and dusted with colored saw dust and lichen trees and bushes-which was the norm for the best "serious" layouts that appeared in Model Railroader and RMC at the time.) He coined the term "Hi Rail" because the rails on his stock Lionel track with extra ties added were so much larger than what "Serious O Gaugers" used at the time. At that time, when the term originated, it meant using toy trains in some combination with "Scale" elements to achieve a less toy like and more realistic appearance.
Personally, I prefer the terms "AF Compatible" and "Scale", with the understanding that anything that is marked "AF Compatible"will run through Gilbert switches and negotiate 20"" radius curves or if track, it will accommodate Gilbert AF original rolling stock and engines and anything marked "Scale" will negotiate "scale" switches or, if track, will accommodate scale flanges.
At least, then you know what you are buying will work on whatever kind of track that you have, or the track will accommodate the rolling stock that you have.
My personal bias is that if a definition does not have "operational utility", it is a bad definition. Just my opinion.
Little Tommy