The word 'vichyssoise' is a direct borrowing from 20th-century French, where it was coined to name a soup associated with the French spa town of Vichy. The suffix '-ois(e)' is a common French adjectival ending meaning 'of or from a place', thus 'vichyssoise' literally means 'from Vichy' or 'in the style of Vichy'. While the soup's exact origins are debated, its name was popularized in the United States by French chef Louis Diat in the early 20th century, who named his creation of a cold leek and potato soup after his hometown region. The term thus traveled from a geographical identifier in French to a specific culinary term in English, retaining its French spelling and pronunciation.

This word is a loanword from French, adopted as a single lexical unit. It is a toponym, derived from the city of Vichy, France, with the addition of the French feminine suffix '-oise'.