Ó

Ó (lowercase ó) is a letter of the Latin script consisting of the letter O with an acute accent (´) above it. In Unicode it is encoded as U+00D3 LATIN CAPITAL LETTER O WITH ACUTE and U+00F3 LATIN SMALL LETTER O WITH ACUTE in the Latin-1 Supplement block, and it is used with distinct meanings in languages including Spanish, Portuguese, Irish, Polish, Hungarian, Icelandic, Czech, Slovak, Catalan, Galician, Dutch, and Italian.^{1 • 2}

Encoding

Ó and ó are precomposed characters: each occupies a single code point so that legacy character sets and text processing can treat the accented letter as one unit. The same visual letter can also be written as a base letter followed by a combining acute accent, O followed by U+0301, and the two forms are canonically equivalent under Unicode normalization.^{1 • 6} The characters descend from ISO/IEC 8859-1 (Latin-1), whose layout Unicode follows up to U+00FF, and both were present in Unicode 1.0's Latin-1 tables under the names LATIN CAPITAL LETTER O ACUTE and LATIN SMALL LETTER O ACUTE.^{7 • 8}

The acute-on-O family extends beyond the Latin-1 pair. Hungarian uses the double acute Ő/ő (U+0150 and U+0151), and Latin Extended Additional contains combinations such as Ṍ/ṍ (O with tilde and acute) and Ṓ (O with macron and acute).^{4 • 9}

Uses across languages

The same glyph carries different instructions in different writing systems, so its meaning must be read in context.¹⁰

• Portuguese. The acute marks an open vowel and the circumflex a closed one, producing minimal pairs such as avó (grandmother) with ó and avô (grandfather) with ô.¹¹
• Irish. Ó is the traditional patronymic prefix in surnames such as Ó Néill (anglicized O'Neill) and Ó Conaill (O'Connell); the acute here is the síneadh fada length mark.^{12 • 5} In Irish orthography the acute accent is the only diacritic normally used.¹³
• Hungarian. Ó marks a long back vowel, distinct from the short o and from the long front vowel ő written with a double acute.⁴ Hungarian is a language in which the diacritic carries a dual function, encoding both vowel length and vowel quality, so it carries more phonetic information than a mark that signals stress alone.¹⁴

Most languages using the Latin script treat letters with diacritical marks as variations of the base letter rather than as fully independent letters of the alphabet, though individual languages differ in how they alphabetize and how much phonetic weight the mark carries.¹⁵

Historical background

The acute and grave accents trace back to systems for marking pitch in ancient writing, later repurposed by European languages to mark stress and vowel quality. Scribes added such signs above letters by hand to guide pronunciation, mark stress, or abbreviate, without any fixed inventory of characters; fixed sets of accented letters emerged with national printing traditions, and typewriter-era dead keys, which struck an accent without advancing the carriage, are the mechanical ancestors of today's keyboard shortcuts.¹⁶

Typing and practical handling

Because Ó is not on the standard English keyboard, several input routes exist: HTML entities (ó or ó), the Windows Alt code Alt+0243 for ó, and dead-key or compose sequences on international layouts.⁵ In text processing, the choice between the precomposed character and the O-plus-combining-accent sequence matters for searching, sorting, and display, since normalization forms differ in which they prefer.⁶ Accented letters in family names also create practical variation: the presence or absence of an accent can change how a surname such as García is recorded in different administrative contexts.¹⁷

References

1. C1 Controls and Latin-1 Supplement, Unicode 18.0.0 NamesList
2. Latin letters, EU Vocabularies, Publications Office of the EU
3. U+00D3, Codepoints
4. The Unicode Standard, Version 17.0, Latin Extended-A chart
5. Alt Codes for Letter O with Accents
6. U+00D3 Latin Capital Letter O with Acute, unicodecharacter.org
7. The Unicode Standard, Version 12.1.0, Chapter 7
8. Unicode Version 1.0 Character Codes (00F4 block)
9. Latin Extended Additional, Unicode 18.0.0 NamesList
10. How Accented O Changes Pronunciation, O With Accent
11. How Awareness of Orthographic Transparency Benefits the Lexical Encoding of Second Language Vowels, Language Learning
12. The Oxford Guide to Style
13. The alphabet, UNGEGN Working Paper 65
14. Just a mark: Diacritic function does not play a role in the early stages of visual word recognition, Behavior Research Methods
15. Chapter 7, The Unicode Standard, Version 18.0.0
16. A Short History Of The Accented O, O With Accent
17. Orthographic variations in family names, familynames.org

Initially written Sep 17, 2026 · Reviewed: Oct 25, 2026 · Edited: Oct 15, 2026; Oct 25, 2026

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