"Ain't gonna happen!"

NODICE

Think of a phrase you’d shout when someone suggests rolling for an impossible outcome.

The phrase "Ain't gonna happen!" is a casual way to say something definitely won’t occur, often shortened to "no way" or "no dice." Here, "no dice" is split into "NODICE" as a single word for the crossword answer, playing on the slang term’s literal meaning (originally from gambling, where "no dice" meant no luck or no chance). The clue leans on the informal tone of the phrase to hint at the compacted answer.