smoke

Smoke is the gray or black substance that goes up into the air when something burns.

Example: The smoke from that factory is making me sick.

A cigarette.

A light grey colour tinted with blue.

If somebody is smoking, they are breathing in smoke, usually from a cigarette.

Example: Excuse me, you can't smoke in the restaurant.

If something is smoking, it is making smoke.

Example: The fire's still smoking. You'd better put some more water on it.