[(US: /lɪˈkɜːr/; UK: /lɪˈkjʊər/; French: [likœʁ])] noun
A liqueur (US: /lɪˈkɜːr/; UK: /lɪˈkjʊər/; French: [likœʁ]) is an alcoholic drink composed of distilled spirits and additional flavorings such as sugar, fruits, herbs, and spices. Often served with or after dessert, they are typically heavily sweetened and un-aged beyond a resting period during production, when necessary, for their flavors to mingle.
Liqueurs are historical descendants of herbal medicines. They were made in Italy as early as the 13th century, often prepared by monks (for example, Chartreuse). Today they are produced the world over, commonly served neat, over ice, with coffee, in cocktails, and used in cooking.
Collins Dictionary Definition:
A liqueur is a strong alcoholic drink with a sweet taste. You drink it after a meal.
A usually sweetened alcoholic liquor (such as brandy) flavoured with fruit, spices, nuts, herbs, or seeds.