A few years ago, we were on a multi-city tour for work. In the second to last town, I remarked that this was our penultimate stop. Later on that evening, Mark wanted to join in the fun and told somebody else that this was our pentangelum stop.
I was lost, mainly because that is not a real word. It's a flaw to use an incorrect word, but it's a skill to invent new words whole cloth. Not wanting to lose pentangelum to the ether, we decided to craft a definition for it.
pen-tan-ge-lum [pen-tan-GEH-lum] - noun
Something that is almost impossible, but not quite.
pen-tan-ge-leous - adj.