flop (v.) Look up flop at Dictionary.com
c.1600, "to flap," probably a variant of flap with a duller, heavier sound. Sense of "fall or drop heavily" is 1836; that of "collapse, fail" is 1919; though the figurative noun sense of "a failure" is recorded from 1893. Related: Flopped; flopping.
flop (n.) Look up flop at Dictionary.com
1823, "act of flopping; any action that produces the sound 'flop;' the sound itself," from flop (v.). Figurative sense of "a failure; that which is a failure" is by 1893, from the notion of a sudden break-down or collapse. Extended form flopperoo attested from 1936.