It's a usage thing, not the technical definition. My point was we didn't use 'debris', even in the context of picking up a bolt. We would refer to it as a piece of FOD, with the acronym still meaning 'damage'. Nonsensical perhaps, but that was the usage. Also it was the norm to say an engine had FOD damage (f.o.damage damage), not that that made any sense. A quick google will see lots of military references using these forms. I think outside the military where things had to make more sense, 'debris' is used, my guess it came after the term FOD was in use and was fit to the acronym, not the other way around.