This doesn't support your assertion- in fact it does the opposite. The definition(s) of inflation has changed over time. That does not make the current definition(s) less correct

Well I did try to caveat it that its one of the few sources I could even find that reference the fact that the definition was changed.

My argument isn't with the fact that "inflation" is in fact being used to mean "price increase of goods." My issue is that economists co-opted the word at all and made it functionally useless, especially in isolation as it is often mentioned with no other context of why prices changed.

The use of "inflation" to mean money supply increase goes all the way back to the roman empire.

“Inflation” is measured based on the prices of a predefined list of goods.

Have you ever read up on that list of predefined goods? It is pretty interesting to see how regularly the list is changed and how many different factors they add in to adjust prices.

Someone did a study looking at magazine prices for example. They picked magazines because they almost always had prices printed on the cover and cover images are cataloged. I don't remember the exact numbers, but they found that the actual prices went up by a much higher rate than how the CPI calculated it because they were discounting price increase with a claim that quality got better. Meaning you may have seen the price double over time but the CPI only said it went up by 30% because you got more value from the newer issues.