A martini is called "dry" primarily because it contains very little vermouth, making the gin (or vodka) the dominant flavor. The term "dry" in this context refers to the low amount of dry vermouth added to the cocktail, not the sweetness level of the vermouth itself. Typically, a dry martini has a ratio of about 6 parts gin to 1 part vermouth, though this can vary, with "extra dry" martinis having just a splash or even only a glass rinse of vermouth

. Historically, the amount of vermouth in martinis has decreased over time. In the 1920s, a dry martini might have had a 3:1 ratio of gin to vermouth, which evolved to 4:1 in the 1940s, and by the late 20th century, 5:1 or 6:1 ratios became common. Some enthusiasts even push this ratio further to 8:1 or more, calling these "drier" martinis

. In summary, what makes a martini dry is the minimal use of vermouth, emphasizing the spirit (gin or vodka) and resulting in a cocktail with a strong, less sweet, and more bitter flavor profile