This word might sound like a particularly arduous skinny-dip, but, sadly, it's not.
Nudiustertian refers to the day before yesterday.
Yes, I agree: it is unusable in normal conversation.
It might be good fun to use among friends, though: our nudiustertian walk took us up onto Sheethanger Common.
On a practical level, you can probably feel quite pleased with yourself if you can remember anything at all about the day before yesterday, and the word should probably be prescribed by doctors as brain-preserving.
What was your nudiustertian dinner?*
Answering that would be a good every day mental exercise for all of us.
Word To Use Today And Probably Quite A Lot On Other Days, Too: nudiustertian. This word was made up by Nathaniel Ward (1578-1652) in his 1647 book The Simple Cobler of Aggawam in America.
The word comes (it is assumed) from the Latin nudius tertius, which means the third day. (Romans counted like musicians: what we would now usually call zero is called one.) The Latin dies means day, nudius means the day before, and tertius means third.
The Latin word nugae is to do with nonsense, and there's probably a bit of that implied in the word, too.
*Butternut squash and blue cheese stew, as it happens.