OXYGEN

[noun] [U] - a colourless gas that forms a large part of the air on Earth and which is needed by most living things in order for them to liveThe air has less oxygen in it at high altitudes than it does at low altitudes.If people are deprived of oxygen, they either suffer brain damage or die.Oxygen masks are pieces of equipment which can be put over a person's nose and mouth to supply oxygen. They can be used by passengers on an aircraft to help them breathe in an emergency, or by ill people who are having difficulty breathing.An oxygen tent is a clear covering put over the head and upper body of an ill person to provide oxygen to help them breathe.