The name mayonnaise is derived from 'sauce mahonnaise', or the sauce from Mahón. Mahón is a place on the Spanish island of Menorca (Minorca).
It is not clear exactly how the sauce got its name. The following story is mentioned:
In 1707 the English conquered the island, which occupies a strategic position in the Mediterranean. In 1756, the French captured the island from the English and established their headquarters in Mahón. The English laid siege to the city, causing the provision situation to deteriorate sharply. As a result, the cook had to improvise and the few ingredients in stock made a cold sauce. This sauce was popular and became known as the sauce mahonnaise after the topping.