ox·y·gen 
/ˈɑ:ksɪʤən/ noun
/ˈɑ:ksɪʤən/ noun [noncount] : a chemical that is found in the air, that has no color, taste, or smell, and that is necessary for life
▪ breathing pure oxygen — often used before another noun ▪ an oxygen tank ▪ The doctors monitored oxygen levels in her blood.
▪ breathing pure oxygen — often used before another noun ▪ an oxygen tank ▪ The doctors monitored oxygen levels in her blood.
