Right but it seemed like it didn't work metaphorically because a pretty important part of the definition -- something present every time I saw the term used -- is that you're in debt to someone else, usually with the connotation of them being able to take the collateralized asset. Yet there was no sense in which that relationship would apply to Boeing and Airbus.

Every other time someone was behind, they were just "behind" -- never saw that prompt the use of a legalistic French term the way that "being in arrears" did.

Edit: O...kay, getting some pushback on this. Let me try to explain with another analogy.

Let's say I saw a comment that read, "He got involved in human trafficking because he has a mortgage."

I had only ever seen "mortgage" used to referred to a secured loan for a home.

So I'd interpret the statement to mean, "he has a big debt he wants to pay and needs money and that motivated him to do slimy things for it."

But let's further say I had specific knowledge that that guy had paid off his home loan years ago. Then I'd be confused and say so, "uh, what? He doesn't even have a mortgage."

Then a bunch of people respond to say, "oh, duh, 'mortgage' comes from the French 'death pledge'[1] -- here they were talking about how he had pledged his life to serve the cartels on pain of death." "Oh, yeah, man, I use 'mortgage' all the time to refer to a blood oath."

That ... would definitely be news to me. Sure -- I wasn't aware of people who had used it the other way. But do you see why I would never have abstracted "mortgage" to refer to death pledges in general, even with great abstraction skills?

Note: "Mortgage", to my knowledge, is not used in English in this other way -- I'm just conveying the sense of surprise there to learn that, had it actually been true.

[1] https://www.lexico.com/en/definition/mortgage