Merriam-Webster's Collegiate® Dictionary, 11th Edition
MUG
I. noun
Etymology: origin unknown
Date: 1664
a cylindrical drinking cup,
2. the face or mouth of a person, grimace , mug shot ,
3. a. chiefly British fool , blockhead , a person easily deceived, punk , thug , mugful noun
II. verb (mugged; mugging)
Date: 1855
intransitive verb to pose or make faces especially to attract attention or for a camera, transitive verb photograph ,
III. transitive verb (mugged; mugging)
Etymology: probably from earlier mug to strike in the face, perhaps from 1mug
Date: circa 1864
to assault usually with intent to rob, to attack suddenly ; bushwhack , muggee noun