flip-flop

Concise Oxford English Dictionary © 2008 Oxford University Press:
flip-flop

▶noun

• 1 a light sandal with a thong that passes between the big and second toes.

• 2 N. Amer. a backward somersault or handspring.

• 3 N. Amer. informal an abrupt reversal of policy.

• 4 Electronics a switching circuit which works by changing between two stable states.

▶verb

• 1 move with a flapping sound or motion.

• 2 N. Amer. informal make an abrupt reversal of policy.

– origin C17: reduplication of flop.