floater, n.² — Green’s Dictionary of Slang

floater n.²

[orig. Oxbridge use; ? corruption of Fr./SE faux pas as ‘foper’, thence ‘floater’; SE float, to circulate a rumour]

an error, a faux pas.

1913		A. Lunn Harrovians 78: It is only when he reaches the university that he realizes that such banter is often a ‘floater’.
1934		Wodehouse Right Ho, Jeeves 1: I see that I have made the second of these two floaters.
1949		Wodehouse Mating Season 72: She will be warned against making any floaters.
1951		G. Greene End of the Affair 44: If only he weren’t quite so serious, sir, but he does take it to heart when I make a floater.
1967		W. Murray Sweet Ride 54: His serve was a floater.
1971		Wodehouse Much Obliged, Jeeves 97: His agony on finding that he has at last made a floater will be frightful.
2003		G. Dyus Jigajig 58: A vague sense of uneasiness came over him as he scoured his mind for a recollection of having made a floater but nothing came to him.