flip-flop (n.)

also flip flop, "plastic thong beach sandal," by 1970, imitative of the sound of walking in them. Flip-flap had been used in various senses, mostly echoic or imitative of a kind of loose flapping movement, since 1520s:

Flip-flaps, a peculiar rollicking dance indulged in by costermongers, better described as the double shuffle; originally a kind of somersault. [Hotten's Slang Dictionary, 1864]

Flip-flop in the general sense of "complete reversal of direction" dates from 1900; it began to be used in electronics in the 1930s in reference to switching circuits that alternate between two states. As a verb by 1897. Flop (n.) in the sense "a turn-round, especially in politics" is from 1880.

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Definitions of flip-flop from WordNet
flip-flop (n.)
a decision to reverse an earlier decision;
Synonyms: reversal / change of mind / turnabout / turnaround
flip-flop (n.)
a backless sandal held to the foot by a thong between the big toe and the second toe;
Synonyms: thong
flip-flop (n.)
an electronic circuit that can assume either of two stable states;
flip-flop (n.)
a backward somersault;
flip-flop (v.)
reverse (a direction, attitude, or course of action);
Synonyms: interchange / tack / switch / alternate / flip