1. The 15th letter of the Roman alphabet
   "He drew a perfect O in the sand";
   - O

1. A nonmetallic bivalent element that is normally a colourless, odourless, tasteless, nonflammable diatomic gas; constitutes 21 percent of the atmosphere by volume; the most abundant element in the earth's crust
   - oxygen, atomic number 8
    
2. The blood group whose red cells carry neither the A nor B antigens
   "people with type O blood are universal donors";
   - type O, group O

1. Used to express surprise;
   "O, it was half the price last time I was here!"";
   - bejeezus [N. Amer, informal], Christ [informal], Christmas [informal], crikey [Brit, informal], cripes [informal], cor [Brit, informal], crumbs [Brit, informal], gosh [informal], golly [informal], by George [informal], by Jove [informal], blimey [Brit, informal], gorblimey [Brit, informal], cor blimey [Brit, informal], my [informal], holy cow [informal], holy mackerel [informal], holy smoke [informal], holy moley [informal], holy moly [informal], fancy [Brit, informal], good grief [informal], goodness [informal], goodness me [informal], Gordon Bennett [informal], gracious [informal], gracious me [informal], fancy that [informal], gawd [informal], god, my word, oh, ah, oh boy [informal], jeez [informal], geez [informal], strewth [Brit, informal], struth [Brit, informal], yikes [informal], I'll be blowed [Brit, informal], blow me [Brit, informal], heck [informal], blooming heck [Brit, informal], jeepers [informal], jeepers creepers [informal], Lord [informal], Lordy [informal], marry [archaic], well I never [informal], heavens [informal], good heavens [informal], my goodness [informal], Jesus [informal], bejesus [N. Amer, informal], od [archaic]

Derived forms: os, Os

Type of: alphabetic character, blood group, blood type, chemical element, element, gas, letter, letter of the alphabet

Part of: air, H2O, Latin alphabet, ozone, Roman alphabet, water

Encyclopedia: O, Promise Me