1. A mixture of nitrogen, oxygen, argon, carbon dioxide, and other gases that make up the earth's atmosphere.

In ancient times, the name used for a gas.

2. The mixture of gases that make up the earth's atmosphere.

The principal gases that compose dry air are: Nitrogen, 78.09%; Oxygen, 20.95%; Argon, 0.93%; and Carbon Dioxide, 0.033%.

Another important constituent of air is water vapor which varies from 0% to about 4%.

A body of air in the lower atmosphere, which is more or less at a constant temperature and moisture content, and is often bounded by cold and warm fronts.

Equal to the cosine of the zenith angle or that angle from directly overhead to a line intersecting the sun.

The air mass is an indication of the length of the path solar radiation travels through the atmosphere. An air mass of 1.0 means the sun is directly overhead and the radiation travels through one atmosphere (thickness).

Measured with a barometer, the force per unit area that the air exerts on any surface; it results from the collision of air molecules.

A gesture made by raising and flexing the index and middle fingers of both hands which is used as quotation marks used to call special attention to a spoken word or expression.

The thin-walled expansion of the tracheal system of an arthropod, which increases or strengthens the inspiration and the exhalation of air.

Air sacs also give buoyancy to aquatic insects, and in dragonflies, it provides insulation around the thoracic wing muscles.

To make a kissing gesture at someone without touching.

Air that is held at a pressure higher than standard atmospheric pressure, thereby increasing its density.

"In 1695, Guillaume Amontons, designed a thermometer using a glass tube filled with compressed air and then topped off with a level of mercury."

A fuel cell technology that uses metals; such as, zinc, aluminum, and magnesium in place of hydrogen to provide electrical power in order to overcome certain disadvantages that are associated with hydrogen as a fuel.

1. A firearm which has a long barrel and that is held against a person's shoulder when he or she is shooting it: Hunters around the world use rifles to kill various "wild-game animals" to be used for food or for a so-called "sport".

Brenda's father took his rifle out to go hunting for deer.

2. A BB gun that uses compressed air or gas to fire small pellets: Lucinda's young brother took his air rifle to shoot at some cans lined up on a fence.
3. A weapon that can shoot many bullets quickly and which is designed for use by the military: A unit of soldiers were armed with assault rifles and they were having target practice with these weapons.