The difference between Bullet and Slug

Bullet as a noun:

A projectile, usually of metal, shot from a gun at high speed.

Bullet as a noun (informal):

An entire round of unfired ammunition for a firearm, including the projectile, the cartridge casing, the propellant charge, etc.

Bullet as a noun:

Ammunition for a sling or slingshot which has been manufactured for such use.

Bullet as a noun (typography):

A printed symbol in the form of a solid circle, (•), often used in lieu of numbers for marking items in a list. (see also bulleted)

Bullet as a noun (banking, finance):

A large scheduled repayment of the principal of a loan; a balloon payment.

Bullet as a noun:

A rejection letter, as for employment, admission to a school or a competition.

Bullet as a noun (slang):

One year of prison time

Bullet as a noun (slang):

An ace (the playing card).

Bullet as a noun (figuratively):

Anything that is projected extremely fast.

Bullet as a noun (in attributive use):

Very fast .

Bullet as a noun (obsolete):

A small ball.

Bullet as a noun (obsolete):

A cannonball.

Bullet as a noun (fishing):

A plumb or sinker.

Bullet as a noun (obsolete):

The fetlock of a horse.

Bullet as a noun (Ireland, particularly in Northern Ireland):

The heavy projectile thrown in a game of road bowling.

Bullet as a verb (transitive, informal):

To draw attention to (text) by, or as if by, placing a graphic bullet in front of it.

Bullet as a verb (intransitive, informal):

To speed, like a bullet.

Bullet as a verb (transitive, informal):

To make a shot, especially with great speed.

Slug as a noun:

Any of many terrestrial pulmonate gastropod mollusks, having no (or only a rudimentary) shell.

Slug as a noun (obsolete):

A slow, lazy person; a sluggard.

Slug as a noun:

A bullet (projectile).

Slug as a noun:

A counterfeit coin, especially one used to steal from vending machines.

Slug as a noun:

A shot of a drink, usually alcoholic.

Slug as a noun (journalism):

A title, name or header, a catchline, a short phrase or title to indicate the content of a newspaper or magazine story for editing use.

Slug as a noun (physics, rarely used):

the Imperial (English) unit of mass that accelerates by 1 foot per second squared (1 ft/s²) when a force of one pound-force (lbf) is exerted on it.

Slug as a noun:

A discrete mass of a material that moves as a unit, usually through another material.

Slug as a noun:

A motile pseudoplasmodium formed by amoebae working together.

Slug as a noun (television editing):

A black screen.

Slug as a noun (metal typesetting):

A piece of type metal imprinted by a linotype machine; also a black mark placed in the margin to indicate an error; also said in application to typewriters; type slug.

Slug as a noun (regional):

A stranger picked up as a passenger to enable legal use of high occupancy vehicle lanes.

Slug as a noun (US, slang, District of Columbia):

A hitchhiking commuter.

Slug as a noun (web design):

The last part of a , the displayed resource name, similar to a filename.

Slug as a noun (obsolete):

A hindrance, an obstruction.

Slug as a noun:

A ship that sails slowly.

Slug as a noun:

A hard blow, usually with the fist.

Slug as a verb:

To drink quickly; to gulp; to down.

Slug as a verb (transitive):

To hit very hard, usually with the fist.

Slug as a verb:

To take part in casual carpooling; to form ad hoc, informal carpools for commuting, essentially a variation of ride-share commuting and hitchhiking.

Slug as a verb (intransitive, of a bullet):

To become reduced in diameter, or changed in shape, by passing from a larger to a smaller part of the bore of the barrel.

Slug as a verb (obsolete, intransitive):

To move slowly or sluggishly; to lie idle.

Slug as a verb (transitive):

To load with a slug or slugs.

Slug as a verb:

To make sluggish.