done deal, a

An irreversible agreement, a final decision or compact. This relatively new synonym for the long-used FAIT ACCOMPLI  dates only from the late  1970s, but  according  to William  Safire, it  had  a  near  predecessor  in  a done  thing. The  latter  surfaced  about  1700, and  Dickens  used  it: “It  was  a done  thing  between  him  and  Scrooge’s  nephew” (A  Christmas  Carol,  1843). The current cliché is also often used in the negative (not a done deal), as in

“We can interview another architect; it’s not a done deal, you know.”