muddle, v.: to combine ingredients, usually in the bottom of a mixing glass, by pressing them together with a muddler before the majority of liquid ingredients are added.
Examples of when this method is applied:
For a mojito sugar, fresh mint leaves and club soda are muddled.
Limes are often muddled with sugar syrup or other fruit as in a Caipirnha and Bésame.
You muddle a sugar cube and bitters in cocktails such as Sazarac and Old-Fashioned.