Y with Accent: ý as Long i, ỹ as a Tone, ŷ as a Welsh Roof

What does the accent on a y do in each language?

An accent on a y does a different job in almost every language that writes one. It can lengthen the vowel, keep a spelling from history, turn y into a consonant, give the word a tone or split two vowels. So before you pick a y with accent, ask which language you are writing. The sounds in the table come from Wiktionary's entries for ý (opens in a new tab), ÿ (opens in a new tab), ŷ (opens in a new tab), ỳ (opens in a new tab) and ỹ (opens in a new tab).

Letter	Language	What the mark does	How it sounds
ý	Czech, Slovak	makes the vowel long	/iː/, the same as í
ý	Icelandic	keeps an older spelling	[iː], the same as í
ý	Faroese	a letter of its own	/ʊiː/, the same as í
ý	Turkmen	makes y a consonant	/j/, as in yes
ý, ỳ, ỷ, ỹ, ỵ	Vietnamese	carries a tone	the tone of the mark
ỹ	Guarani, Kaingang	makes the vowel nasal	/ɨ̃/ in Guarani, /ʌ̃/ in Kaingang
ŷ	Welsh	makes the stressed vowel long	/ɨː/ in the north, /iː/ in the south
ÿ	French	says y apart from the vowel before it	/i/

Read the table by language, not by letter. The same ý is a long vowel in Slovak and a consonant in Turkmen. Only the Turkmen ý sounds like the English letter, and there it is a consonant.

Why do Czech and Slovak write ý where í sounds the same?

Because the letter tells the reader something the sound does not. The Czech Language Institute's language handbook (opens in a new tab) says the sounds [i] and [í] are written with i, í or y, ý. The consonant before the vowel decides which. The Slovak spelling rules (opens in a new tab) add a second signal: an adjective ending in ý is singular.

Rule	Language	Words with the accented y
After h, ch, k and r, native words write y or ý	Czech	drahý, lichý, hezký, dobrý
After d, t and n, ý keeps the consonant hard	Czech	dým, týden, čistý, černý
After ž, š, č, ř and j, only i or í	Czech	none: život, číslo, říjen
The prefix vý-	Slovak	výber, východ
ý for one, í for many, in pekný-type adjectives	Slovak	pekný chlapec, pekní chlapci

The d, t, n row is the clever one. With i or í, the consonant is soft, as in dítě or tisíc. With ý, the d of dým and the t of týden stay hard. Borrowed words follow their own rules.

The Slovak plural signal shows only in writing. Pekný chlapec is singular and pekní chlapci is plural, yet both endings sound alike. Adjectives of the cudzí type keep í in both.

Sometimes the accented y is all that keeps two words apart. Wiktionary lists výt (opens in a new tab), to howl, and vít (opens in a new tab), to weave, as homophones. Search is less strict. Under Czech sorting rules in Node.js v26 (ICU 78.3, CLDR 48), ý matches y when accents are ignored, and ý does not match í.

How does Icelandic choose between í and ý?

From a related word. Ritreglur (opens in a new tab), the official Icelandic spelling rules, say in § 6 that older Icelandic said i and y differently. Speech lost the difference, and spelling kept it. So the writer looks for a relative: ý goes where a related word has ú, jú or jó.

Word with ý	Related word that decides it
hýsa	hús, with ú
rými	rúm, with ú
dýpi	djúpur, with jú
sýna	sjón, with jó
lýsa	ljós, with jó

The pairs come from § 6.2.2. Where no relative helps, the rules send the writer to a dictionary. They also list homophones spelled apart, such as híði and hýði; the second goes with húð.

The letter still counts as its own. Unicode's Icelandic sorting rules (opens in a new tab) file ý after y and before z and þ. Our Node.js sort of i, í, y, ý, z and þ kept that order.

Faroese keeps the pair with a different sound. Wiktionary gives Faroese ý as /ʊiː/, a homophone of í.

Which Vietnamese tone does each y carry?

In Vietnamese, the mark on a y with accent is a tone. Plain y has no mark. Wiktionary describes each marked letter as the letter y in its tone, and dấu sắc (opens in a new tab) names the acute as the sắc tone. The places come from the facts on this page.

Letter	Mark	Tone	A place with it
ý	acute	sắc	Phủ Lý, Phú Quý
ỳ	grave	huyền	Tam Kỳ, Kỳ Anh
ỷ	hook above	hỏi	Bản Na Hỷ
ỹ	tilde	ngã	Mỹ Tho, Phú Mỹ
ỵ	dot below	nặng	none in the facts

The entries for ỷ (opens in a new tab) and ỵ (opens in a new tab) give the hỏi and nặng tones. The ỹ entry calls its mark a perispomene for the ngã tone.

Vietnamese y has a twin. Many words are written with y or i. Wiktionary lists Mỹ (opens in a new tab), America, as an alternative spelling of Mĩ, and kỹ (opens in a new tab), careful, as one of kĩ. Place names in the facts keep the y.

That twin matters in search. Under Vietnamese rules, in the same Node.js check, a search that ignores marks matches Mỹ with My and Mý. It does not match Mỹ with Mĩ, because y and i are different letters. If your data mixes both spellings, search for both.

ỹ is not only Vietnamese. Wiktionary lists it in Paraguayan Guarani as the nasal vowel /ɨ̃/ and in Kaingang as /ʌ̃/. There the tilde marks a nasal vowel, not a tone.

Where does French still write ÿ?

Almost only in proper names. The French Wiktionnaire's entry for ÿ (opens in a new tab) says the y with umlaut is said on its own, not as part of a pair with the a or o before it. It adds that ÿ appears only in proper names and their derivatives. L'Haÿ-les-Roses (opens in a new tab) is said /la.i/. The writer Pierre Louÿs (opens in a new tab) took his ÿ as a variant of Louis.

We read the French government's full commune list through the API Découpage administratif (opens in a new tab) on 2026-10-09. These are the only communes with ÿ:

• Aÿ-Champagne, in the Marne
• Faÿ-lès-Nemours, in Seine-et-Marne
• L'Haÿ-les-Roses, in the Val-de-Marne
• Moÿ-de-l'Aisne, in the Aisne

The same scan for ï found many more names, so it could find a letter. Under French rules in Node.js, Haÿ matches Hay when accents are ignored. A search box will usually forgive a missing ÿ.

The capital Ÿ is rarer still, and old code pages show it. The table reads the Unicode mapping files for ISO 8859-1 (opens in a new tab), ISO 8859-15 (opens in a new tab) and Windows-1252 (opens in a new tab).

	ÿ	Ÿ
Unicode code point	U+00FF	U+0178
ISO 8859-1, Latin-1	byte FF	missing
ISO 8859-15	byte FF	byte BE
Windows-1252	byte FF	byte 9F
Windows Alt code	Alt+0255	Alt+0159

Latin-1 has the small ÿ and no capital. Each Alt code on this page is the Windows-1252 byte in decimal: FF is 255 and 9F is 159. That is why this accented y and its capital have codes so far apart.

What does ŷ mean in Welsh and in statistics?

In Welsh, ŷ is a y with a to bach, a long stressed vowel. In statistics, ŷ is y hat, the value a model predicts. Wiktionary's entry for to bach (opens in a new tab) translates the name as little roof. Bangor University (opens in a new tab) lists the vowels that take it: â, ê, î, ô, û, ŵ and ŷ.

Welsh writes y with a to bach, an acute, a grave or a diaeresis. Each mark says something different about the vowel. The table follows Wiktionary's letter entries, northern sound first.

Letter	Mark	What it tells the reader	Sound
ŷ	to bach	a long stressed vowel, in a short word or a final syllable	/ɨː/, /iː/
ý	acute	a short vowel in the stressed final syllable of a longer word	/ɨ̞/, /ɪ/
ỳ	grave	the short sound /ə/ in a one-syllable word	/ə/
ÿ	diaeresis	y said as its own syllable, apart from the next vowel	/ɨ̞/, /ɪ/

The best-known ŷ is tŷ (opens in a new tab), house, /tɨː/ in the north. Its plural is tai, and tŷ bach, small house, also means toilet. Compounds drop the roof: the same entry lists gwesty, hotel, and goleudy, lighthouse.

The statistics ŷ is the same character. A regression computes a predicted value for every case. The Berkeley Statistics 151 notes (opens in a new tab) call these fitted values and write them ŷ. The NIST statistics handbook (opens in a new tab) explains the hat: it marks an estimate, not the true value.

For a computer, both are one letter. UnicodeData.txt (opens in a new tab) breaks ŷ down into y plus U+0302, COMBINING CIRCUMFLEX ACCENT. Normalization to NFC joins the two parts back into ŷ, as our Node.js check confirmed. So a y hat pasted from a report and a Welsh ŷ compare equal once both are normalized.