French word mais oui comes from French mais, French oui (Yes Yes.)

Detailed word origin of mais oui

Dictionary entry	Language	Definition
mais	French (fra)	An expression of surprise, disbelief, or frustration roughly equivalent to the English well, or sometimes yeah But.
oui	French (fra)	Yes Yes.
mais oui	French (fra)	Of course.

Words with the same origin as mais oui