alt Hacker Newsunobtainium predates Avatar https://en.wikipedia.org/wiki/Unobtainium
and at least that exposition makes more sense then the "fountain of youth brain juice" in the sequel, when the humans can literally reincarnate themselves without having to cross interstellar space to do it.
My physics teacher in high school used unobtanium in class and was the first I recall using it. This was way before Core or Avatar. After reading your wiki link, it fit perfectly with the definition of a frictionless, massless pulley use.
It's funny, because I'm one to use movie references in casual conversation like it's nothing, yet my use was definitely not in this case