-o

suff.
Used to form an informal, abbreviated, or slang word or variant: ammo.

[Perhaps from OH¹ and from shortenings such as HIPPO.]

Note: click on a word meaning below to see its connections and related words.

The noun has 3 meanings:

Meaning #1: the blood group whose red cells carry neither the A nor B antigens
  Synonyms: type O, group O

Meaning #2: 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
  Synonyms: oxygen, atomic number 8

Meaning #3: the 15th letter of the Roman alphabet

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I O	I O Adapter
Can O Crickets	O. Henry