File has a lot of meanings. Let’s look at them, shall we?
The first file to show up was the metal file. Although the exact date for the noun isn’t known, the verb (to file something down) showed up in the early thirteenthcentury and it came from the noun. The word comes from the Old English feol, file, which is from the Proto Germanic fihalo, cutting tool, and is thought to be from the Proto Indo European peig-, cut or mark with incision. And I know that word has shown up here before.
But there’s also another file, the one related to documents. That couldn’t possible related, could it?
Of course not. That would be ridiculous.
That file first showed up in the mid fifteenth century, both as a verb and a noun. Originally, the noun meant “string or wire on which documents are strung” and the verb was “place papers in consecutive order for future reference”. At least the latter makes sense. It’s from the French file, which could mean file or a row, while the verb is from the Old French filer, which had the documents-on-a-wire definition, but could also mean to spin thread. Both words are related to the Middle French filer (string documents, apparently that was a popular thing in the middle ages), and the Old French fil, thread or string. They’re from the classical Latin filum, wire or thread, and further back the Proto Indo European gwhis-lom, from gwhi-, thread or tendon.
That gwhi- is related to several other words. First there’s profile, which showed up in the mid seventeenth century as the outline of something and comes from the Italian profilo, outline. It’s a mix of the prefix pro-, which is from per- here and means forward, and filare, from the Late Latin filare, to spin or draw out a line. That word is from filum, which of course is from gwhi-. There’s also defile… but not the defile you’re thinking of. That one’s actually related to foul. No, defile the noun is a narrow passage, which makes sense when you remember that file also means row in French.
Other words related to the row/thread file include filament, fillet, and fiber. Will I get to them some day? Probably!
Tony Jebson’s page on the Origins of Old English