oxygen

n. Tasteless odourless gaseous element essential to plant and animal life. [greek oxus sharp, *-gen (because it was thought to be present in all acids)]

n. A colorless, tasteless, odorless, gaseous element occurring in the free state in the atmosphere, of which it forms about 23 per cent by weight and about 21 per cent by volume, being slightly heavier than nitrogen. Symbol O. Atomic weight 15.96.