o

I. noun (plural o's or os) Usage: often capitalized, often attributive Date: before 12th century 1. a. the 15th letter of the English alphabet b. a graphic representation of this letter c. a speech counterpart of orthographic o 2. a graphic device for reproducing the letter o 3. one designated o especially as the 15th in order or class 4. something shaped like the letter O; especially zero II. abbreviation 1. ocean 2. ohm 3. old 4. order 5. over