Mug can be a noun or a verb, with completely different meanings. As a noun, mug is a large cup used for beverages, or the amount contained in it. In everyday language, it can also be used to refer to someone's face and is often preceded by "ugly." As a verb, mug means to attack and rob someone in public, or to make strange expressions with your face.
The girl came down the stairs, holding a huge mug of hot chocolate in her tiny hands.
I'm so mad at him! I don't want to see his ugly mug ever again.
After being mugged, Mary was afraid to go out alone after dark.
beer mug: a clear glass with a handle, used to serve beer; mug shot: an official identification photo of the face, usually taken by police when someone is arrested
Mug is also used as a slang term meaning "mouth." Check out the full definition to find out more.
Many learners confuse the words mug (to attack and steal from someone) and "assault." In English, these two words are related but have different meanings. To "assault" is to attack someone, but it does not imply that the person has been robbed. If you want to describe an attack and robbery in a public space like a street, mug is a better word to use. A person who is mugged is not necessarily hurt, but there is usually a threat of violence.
Scandinavian; compare Swedish mugg, Norwegian, Danish mugge drinking cup; sense "face" apparently transferred from cups adorned with grotesque faces; sense "to assault" from earlier pugilistic slang "to strike in the face, fight." Probably 1560-70.