slug

Concise Oxford English Dictionary © 2008 Oxford University Press:
slug1

▶noun

• 1 a tough-skinned terrestrial mollusc which lacks a shell and secretes a film of mucus for protection. [Order Stylommatophora.]

• 2 an amount of an alcoholic drink that is gulped or poured.

• 3 an elongated, typically rounded piece of metal.

  ■ chiefly N. Amer. a bullet.

• 4 a line of type in Linotype printing.

▶verb (slugs, slugging, slugged) gulp (something, typically alcohol).

– origin ME (in the sense ‘sluggard’): prob. of Scand. origin.

Concise Oxford English Dictionary © 2008 Oxford University Press:
slug2 informal, chiefly N. Amer.

▶verb (slugs, slugging, slugged) strike with a hard blow.

■ (slug it out) settle a dispute or contest by fighting or competing fiercely.

▶noun a hard blow.

– derivatives
slugger noun.

– origin C19: of unknown origin; cf. slog.