O

(LETTER) (plural O's or Os), o (plural o's or os) [noun] [C] - the 15th letter of the English alphabetO is used in speech to mean zero, and is sometimes written as 'oh'.My phone number is three, one, o, five, one, double o (= 3105100).The date 1705 can be pronounced seventeen o five.See study section: ZeroAn O level is a public examination in a particular subject that was taken in the past in British schools by children aged 15 or 16, or the qualification obtained.I failed my History O level.She's got 10 O levels.O levels were replaced by GCSEs in 1988.Compare A level at A.