vietnami (“Vietnamese”) + papucs (“sandal”). These flip-flops were originally imported from Vietnam. Compare Czech and Slovak vietnamky, Ukrainian в'єтнамки (vʺjetnamky) and Russian вьетнамки (vʹjetnamki). It's also possible that it is from Russian.
- flip-flop, thong (a sandal, usually of rubber, secured to the foot by two straps mounted between the big toe and its neighbour)