Wiktionary
n. Air which has been reduced in volume and increased in pressure; it is used to power machinery etc
WordNet
n. air at a pressure greater than that of the atmosphere; "compressed air is often used to power machines"
Wikipedia
Compressed air is air kept under a pressure that is greater than atmospheric pressure. It serves many domestic and industrial purposes.
In Europe, 10 percent of all industrial electricity consumption is to produce compressed air—amounting to 80 terawatt hours consumption per year.
Usage examples of "compressed air".
He pushed the nose of the amatol block back off the wire, but the wire strop securing it to the compressed air cylinder held it in such a position that it remained with its nose nine inches clear of the water.
That's my big idea--Damon's Whizzer --propellers revolving in compressed air like water.
We bleed compressed air under fairly high pressure into the fore part of the ship.
Shrapnel from the first bomb had burst a compressed air cylinder in the torpedo workshop, and Hartley, the man who, above all, had become the backbone of the Ulysses had taken shelter there, only seconds before.
As anyone who has used such a pump knows, compressed air grows swiftly hot, and the temperature below it would rise to some 60,000 Kelvin, or ten times the surface temperature of the Sun.
Shock-absorbing springs and bags of compressed air isolated the people and machines from the granite floors.