Lucka nio

The blessed drink of early morning tea.

88888888Jan Struther (1901-1953)
8888888"Three Stockings"

87

Mug. Cf. Low German mokke, mucke, Norwegian mugga, Norman dialect moque. Origin unknown, but perhaps originally a personal name (cf. jug). Hence perhaps mug, face early mugs often representing grotesque faces. With mug, muff, duffer, cf. crock and also French cruche, in the same sense. To mug up (for an examination) may be an obscure metaphore from theatrical to mug up, make up one's mug (face) with paint.
From "An Etymological Dictionary of Modern English" by Ernest Weekley