gas

Matter in a state intermediate between liquid and plasma that can be contained only if it is fully surrounded by a solid (or in a bubble of liquid) (or held together by gravitational pull); it can condense into a liquid, or can (rarely) become a solid directly.

"A lot of gas had escaped from the cylinder."

Similar: vapor / vapour

A chemical element or compound in such a state.

"The atmosphere is made up of a number of different gases."

A flammable gaseous hydrocarbon or hydrocarbon mixture (typically predominantly methane) used as a fuel, e.g. for cooking, heating, electricity generation or as a fuel in internal combustion engines in vehicles.

"Gas-fired power stations have largely replaced coal-burning ones."

To kill with poisonous gas.

To talk in a boastful or vapid way; chatter.

To impose upon by talking boastfully.