Definition: the blood group whose red cells carry neither the A nor B antigens
Usage: people with type O blood are universal donors
Similar words: blood group, blood type
Definition: human blood cells (usually just the red blood cells) that have the same antigens
Definition: the 15th letter of the Roman alphabet
Similar words: alphabetic character, letter, letter of the alphabet
Definition: the conventional characters of the alphabet used to represent speech
Usage: his grandmother taught him his letters
Synonyms: atomic number 8, O, oxygen
Definition: a nonmetallic bivalent element that is normally a colorless odorless tasteless nonflammable diatomic gas; constitutes 21 percent of the atmosphere by volume; the most abundant element in the earth's crust
Similar words: element, chemical element
Definition: any of the more than 100 known substances (of which 92 occur naturally) that cannot be separated into simpler substances and that singly or in combination constitute all matter
Similar words: gas
Definition: a fluid in the gaseous state having neither independent shape nor volume and being able to expand indefinitely