Vermouth (/vərˈmuːθ/, UK also /ˈvɜːrməθ/) is an aromatized fortified wine, flavoured with various botanicals (roots, barks, flowers, seeds, herbs, and spices) and sometimes colored. The modern versions of the beverage were first produced in the mid- to late 18th century in Turin, Italy. While vermouth was traditionally used for medicinal purposes, it was later served as an apéritif, with fashionable cafés in Turin serving it to guests around the clock. In the late 19th century it became popular with bartenders as a key ingredient for cocktails, such as the martini, the Manhattan, the Rob Roy, and the Negroni. In addition to being consumed as an apéritif or cocktail ingredient, vermouth is sometimes used as an alternative to white wine in cooking. Vermouth is produced by starting with a base of a neutral grape wine or unfermented wine must.
Collins Dictionary Definition:
Vermouth is a strong alcoholic drink made from red or white wine flavoured with herbs.
A dry or sweet aperitif wine flavored with aromatic herbs and often used in mixed drinks.