O 1 , o / əʊ $ oʊ / noun ( plural O’s , o’s )
1 [ uncountable and countable ] the 15th letter of the English alphabet
2 [ uncountable ] spoken zero : My phone number is six o four double two (= 60422 ) .
3 [ uncountable ] a common type of blood
zero the number 0. Also used when saying there is nothing at all : A million is written as one followed by six zeros. | a temperature of zero degrees | Our chances of success are virtually zero.
nil British English zero - used especially in the results of sports games : United won the game three-nil. | In rural areas, employment opportunities are almost nil.
nought British English spoken zero – used in calculations and figures : It has increased by nought point seven five per cent (= 0.75% ) .
O used to say the number 0 like the letter O : The code for Oxford is 0 one eight six five (= 01865 ) .
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