Slug

n. worm-like gastropod that is related to the snail but has no shell; insect larvae; round bullet; lazy person (Slang); shot of liquor (Informal); strip of metal used for spacing (Printing); heavy blow

v. hit hard with the fist or with a bat (Slang); move slowly; be idle or lazy

Slug is a common non-scientific word which is most often applied to any gastropod mollusk which has a very reduced shell, a small internal shell, or no shell at all. The word "slug" is used in everyday parlance to differentiate these animals from other gastropods commonly known as snails, but in reality slugs and snails are very often almost exactly similar, apart from the fact that snails usually have a functional coiled shell. The word slug has been commonly applied to some marine species as well as some terrestrial species of shell-less snails.
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Noun
1. a projectile that is fired from a gun
(synonym) bullet
(hypernym) projectile, missile
(hyponym) dumdum, dumdum bullet
(part-holonym) cartridge
2. an idle slothful person
(synonym) sluggard
(hypernym) idler, loafer, do-nothing, layabout, bum
(derivation) idle, laze, stagnate
3. any of various terrestrial gastropods having an elongated slimy body and no external shell
(hypernym) gastropod, univalve
(member-holonym) Limacidae, family Limacidae
Verb
1. strike heavily, especially with the fist or a bat; "He slugged me so hard that I passed out"
(synonym) slog, swig
(hypernym) hit
(derivation) slugger, slogger
2. be idle; exist in a changeless situation; "The old man sat and stagnated on his porch"; "He slugged in bed all morning"
(synonym) idle, laze, stagnate
(hyponym) moon, moon around, moon on
(derivation) sluggard

(v. t.)
To strike heavily.
  

(v. t.)
To make sluggish.
  

(v. t.)
To load with a slug or slugs; as, to slug a gun.
  

(v. i.)
To move slowly; to lie idle.
  

(v. i.)
To become reduced in diameter, or changed in shape, by passing from a larger to a smaller part of the bore of the barrel; -- said of a bullet when fired from a gun, pistol, or other firearm.
  

(n.)
Any smooth, soft larva of a sawfly or moth which creeps like a mollusk; as, the pear slug; rose slug.
  

(n.)
Any one of numerous species of terrestrial pulmonate mollusks belonging to Limax and several related genera, in which the shell is either small and concealed in the mantle, or altogether wanting. They are closely allied to the land snails.
  

(n.)
An irregularly shaped piece of metal, used as a missile for a gun.
  

(n.)
A thick strip of metal less than type high, and as long as the width of a column or a page, -- used in spacing out pages and to separate display lines, etc.
  

(n.)
A ship that sails slowly.
  

(n.)
A hindrance; an obstruction.
  

(n.)
A drone; a slow, lazy fellow; a sluggard.
  

shrewd, shifty, canny, cagey, clever, cunning, sly