flop, n.¹ — Green’s Dictionary of Slang

flop n.¹

[SE flop, i.e. one fig. lets something fall on the person one is cheating]

(orig. US campus)

any action by which someone else is deceived.

1856		B.H. Hall College Words (rev. edn) 204: flop. [...] Any ‘cute’ performance by which a man is sold [deceived] is a good flop.
1914		Jackson & Hellyer Vocab. Criminal Sl. 35: flop [...] used by short changers as a synonym of ‘flim’.