| Oxygen 1. (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. 2. (n.) Chlorine used in bleaching. Thesaurus Entries acetylene, ammonia, argon, asphyxiating gas, butane, carbon dioxide, carbon monoxide, chlorine, coal gas, ethane, ether, ethylene, fluorine, formaldehyde, helium, hydrogen, illuminating gas, krypton, lewisite, marsh gas, methane, mustard gas, natural gas, neon, nitrogen, ozone, poison gas, propane, radon, sewer gas, xenon | ![]() |