[andrewaylett]

Since you mentioned nit-picking, I'll nit-pick :). You mean "die", as in the singular of "dice".

[aaronblohowiak]

I believe it is a reference to die as in manufacturing dies https://en.m.wikipedia.org/wiki/Die_(manufacturing) basically the phrase is like “the mould is set”

[grzm]

I believe your parent has it right: cast in this case means thrown or tossed. "to cause to move or send forth by throwing cast a fishing lure cast dice", sense 1a here:

https://www.merriam-webster.com/dictionary/cast

- https://en.wiktionary.org/wiki/the_die_is_cast

- https://idioms.thefreedictionary.com/die+is+cast

[aaronblohowiak]

fascinating! thank you!

[35bge57dtjku]

Isn't likely to be from dice because it's such an ancient expression, like from Roman times?

[aninhumer]

Yeah https://en.wikipedia.org/wiki/Alea_iacta_est

[hbarka]

Trivial detour. Remani hits the point.