Cheese grater? Who knows what a cheese grater is in a post-apocalyptic wasteland. Couldn't get it out of my mind for the rest of the story. But a good story it was. Except for the cheese grater.
Of course they have cheese graters.
That's what they use to flay people alive with.
People flay other people alive in post-apocalyptic wastelands, right?
Well, then it's not a cheese grater..
Even if it has a new use, the term might stay the same. Language is funny like that...
Example: I have a Xerox monitor, and I've never wanted to make copies of it.
That's not the best example, since Xerox is the brand name, not the object. Unless you have a photocopier monitor. But I agree with your point. I'm not sure what would make the best example. I'm having trouble thinking of objects that fall under this category.
--I guess, perhaps, you could say "glasses" (as in eyeglasses) is a bit outdated because many eyeglasses have no glass in them, but no one would know what you mean if you said "polycarbonates". (would be a better example if I could think of a name based on function rather than composition)
For some reason, expressions are coming to mind, not objects, such as:
a "rule of thumb" has nothing to do with thumbs
"letting the cat out of the bag" has nothing to do with cats or bags
Those aren't great examples either, having more to do with lasting expressions than actual object names.
Maybe they call it a cheese grater to add insult to injury. "Not only am I damaging you, but I'm not even doing it properly and using a human grater, that's how little respect I have for your existence."
Or perhaps the overlords also use them to grate cheese. Nothing like a little blood to season your pizza toppings.