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Not to be confused with Ő, O with double acute.
Õ õ

"Õ", or "õ" is a composition of the Latin letter O with the diacritic mark tilde.

The HTML entity is Õ for Õ and õ for õ.



In Estonian, Õ is the 27th letter of the alphabet (between W and Ä), representing the close-mid back unrounded vowel sound [ɤ]. The vowel had previously been marked with Ö, but in early 19th century, Otto Wilhelm Masing adopted the letter Õ, ending the confusion between several homographs and showing clearly how to pronounce a word.

In informal writing, e.g., emails, instant messaging and when using foreign keyboard layouts where the letter Õ is not available, some Estonians use the characters O or 6 to approximate this letter, and yet others use O followed by a tilde (O~) or the character ø.


In the Portuguese language, the symbol Õ stands for a nasal close-mid back rounded vowel, also written [õ] in IPA. It is not considered an independent letter of the alphabet.


In the Vietnamese language, the symbol Õ stands for the sound [ɔ] with creaky voice (rising tone with a glottal break followed by a continuation of the rising tone). Vietnamese also has derived letters / and /.

Mathematical use

The symbol, pronounced soft-O, is used as a variant of big O notation that ignores logarithmic factors. Thus, f(n) = Õ(g(n)) is shorthand for f(n) = O(g(n)logkg( n)) for some k.

Encoding problems

Due to character encoding confusion, the letters can be seen on many incorrectly coded Hungarian web pages, representing Ő/ő (letter O with double acute accent). This can happen due to said characters sharing a code point in the ISO 8859-1 and 8859-2 character sets, as well as the Windows-1252 and Windows-1250 character sets, and the web site designer forgetting to set the correct code page. Õ and õ are not part of the Hungarian alphabet.

See also

The Basic modern Latin alphabet
Aa Bb Cc Dd Ee Ff Gg Hh Ii Jj Kk Ll Mm Nn Oo Pp Qq Rr Ss Tt Uu Vv Ww Xx Yy Zz
Letter O with diacritics
Letters using tilde sign

history palaeography derivations diacritics punctuation numerals Unicode list of letters ISO/IEC 646


Up to date as of January 15, 2010

Definition from Wiktionary, a free dictionary

See also Ö, õ, and ö



The Latin script
Aa Bb Cc Dd Ee Ff Gg Hh Ii Jj Kk Ll Mm Nn Oo Pp Qq Rr Ss Tt Uu Vv Ww Xx Yy Zz
Variations of letter O

Óó Òò Ŏŏ Ôô Ốố Ồồ Ỗỗ Ổổ Ǒǒ Öö Ȫȫ Őő Õõ Ṍṍ Ṏṏ Ȭȭ Ȯȯ Ȱȱ Øø Ǿǿ Ǫǫ Ǭǭ Ōō Ṓṓ Ṑṑ Ỏỏ Ȍȍ Ȏȏ Ơơ Ộộ Ɵɵ Œœ

Letters using tilde sign or middle tilde sign

Ãã Ĩĩ Ññ Õõ P̃p̃ Ũũ Ṽṽ


Õ upper case (lower case õ)

  1. The letter O with a tilde.



Õ (uppercase, lowercase õ)

  1. The 27th letter of the Estonian alphabet, preceded by W and followed by Ä.

Simple English

The Latin alphabet
Aa Bb Cc Dd
Ee Ff Gg Hh Ii Jj
Kk Ll Mm Nn Oo Pp
Qq Rr Ss Tt Uu Vv
Ww Xx Yy Zz

O is the fifteenth (number 15) letter in the English alphabet.

Meanings for O

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