(slug) noun
1. A bullet or shot of irregular or oblong shape, especially as used in old muskets.
2. Printing a A strip of type metal, thicker than a lead and less than type-high, for spacing matter, etc. b A metal strip bearing a type-high number, abbreviated title, or the like, used as a compositor's mark.
3. A slungshot, or its metal weight.
4. Any small chunk of metal; especially, one used as a coin in automatic machines, as dial telephones.
5. Physics A unit of mass; the mass of a body which, when acted upon by a force of one pound, acquires an acceleration of one foot per second per second: it has the value of about 32.174 pounds or 14.59 kilograms, and is also called geepound.
—v. slugged, slug·ging v.i. To take shape to fit the grooves of a rifle, as a bullet.
—v.t. To load with slugs. [Origin uncertain.? Akin. to SLAG.]

(slug) noun
1. Any of numerous terrestrial gastropod mollusks related to snails but having only a rudimentary shell concealed in the mantle, or none at all.
2. The larva of certain insects, as the sawfly, resembling a slug.
3. A sluggard. [ME slugge a sluggard,? <Scand. Cf. dial. Norw. slugg a large, heavy object.]
SLUG

(slug) Colloq. noun
1. A heavy blow, as with the fist or a baseball bat.
2. A drink of undiluted liquor.
—v.t. slugged, slug·ging To strike heavily or brutally, or without science, as with the fist or a baseball bat. [Origin uncertain]
—slug′ger noun