Re: ‘the die is cast’, it’s an English translation of the Latin ‘alea iacta est’ which does, in plain old English, mean “the die has been thrown”.
I have these stupid epiphanies ALL THE TIME. I only last year realized that “The Bible” means “The Book”. The stupid part? I had been studying ancient Greek, including the word ‘biblion’ which means ‘book’, for several months already.
Three other recent ones:
Carnival = carne-vale, Latin for ‘goodbye, meat’.
Phillip = Phil-hippos, or horse-lover, in Greek. This was just dumb. All I needed to do was add the -os.
Aborginal = I read about a tribe in ancient Italy called the “Aborigines”. ‘Could the English word referring to early/original inhabitants of any place be transference for that?’ I wondered excitedly. I looked it up. The word actually breaks down as ab-origines. Straightforward Latin for ‘from the beginning’. Duh.