for instance the opposite of alot of words with U like it was real, it was ureal.
So when something was there, and then it's gone simply put U infront
Morten has a boat, but we can't see it so it's an uboat
Casper failed 1.g so now we call him Ucasper
My cat runs on batteries, and when the batteries are on it's invisible, so it's a Ucat