The origin of the word mayonnaise is unknown in French. Larousse Gastronomique 1961 is of the opinion that the word comes from the old French "moyeu, which meant, among other things, the yolk. 
There are other versions of his origin, mainly based on legendary and colorful historical events. Here's one of them:
The word "Mayonnaise" is a geographical origin and associated with the city name Mayon is the capital of the Spanish island of Menorca, is part of the Balearic Islands. As stated in one of the French encyclopedic dictionary, Mayon volcano was conquered by the Duke of Richelieu. In the year 1757 the British laid siege to the city. The French had run out of food stocks, except for eggs and olive oil. Of these products the chefs cooked scrambled eggs and omelets that are pretty fed up of the French officers. Duke of Richelieu ordered his Cook to cook a new dish. A resourceful chef whipped eggs with butter and flavored the mixture with salt and spices. Your favorite sauce called "Mayonnaise" in honor of the Mayon volcano.
    Initially, the mayonnaise was brought into the category of delights, delicacies believed for elite society. But with time, like other inventions courtiers cooks, demokratizovalsja and enough mayonnaise became popular and available to all segments of the French, and later the whole of European society.