Webster's Revised Unabridged Dictionary · 1913

Flop

Flop (flop) , transitive verb

[A variant of flap.]

1.
To clap or strike, as a bird its wings, a fish its tail, etc.; to flap.
2.
To turn suddenly, as something broad and flat. [Colloquial] — Fielding

Flop (flop) , intransitive verb

1.
To strike about with something broad and flat, as a fish with its tail, or a bird with its wings; to rise and fall; as, the brim of a hat flops.
2.
To fall, sink, or throw one's self, heavily, clumsily, and unexpectedly on the ground. [Colloquial] — Dickens

Flop , noun

Act of flopping. [Colloquial] — W. H. Russell