U with Accent: ú for Stress, ù Only in Où, û in Sûr, Long ū

What job does the mark on a u with accent do?

The mark on a u with accent does a different job in each language, so pick it by the job. Spanish ú shows the stressed syllable or splits two vowels. French ù and û mostly tell two words apart without changing the sound. Latvian and Lithuanian ū makes the vowel long, the job that Czech, Hungarian and Irish give to ú.

Job of the mark	Letter	Language	Example	Source
Shows the stressed syllable	ú	Spanish	Perú, público	University of Iowa notes
Splits a vowel pair into two syllables	ú	Spanish	continúo, baúl	University of Iowa notes
Separates two words that sound alike	ú	Spanish	tú (you), tu (your)	University of Iowa notes
Separates two words, same sound	ù	French	où (where), ou (or)	OQLF, Wiktionary
Separates two words, same sound	û	French	sûr (sure), sur (on)	Académie française, Wiktionary
Makes the vowel long	ú	Czech, Hungarian, Irish	Irish ú fada, "long u"	Wiktionary
Makes the vowel long	ū	Latvian, Lithuanian	lūpa (lip)	Wiktionary, Lithuanian Encyclopedia

So the first question about any u accent mark is the language. In the Unicode CLDR, the Spanish alphabet holds ú but not ù or û, and the French one holds ù and û but not ú.

When does Spanish put an accent mark on the u?

Spanish writes the u with accent mark, ú, for two reasons. The first is stress. The University of Iowa's notes on the tilde (opens in a new tab) give the pattern. A word ending in a vowel, n or s stresses the next-to-last syllable. A word ending in another consonant stresses the last. A word that breaks the pattern takes the mark, as in Perú. A word stressed third from the end always does, as in público.

The second reason is a vowel pair. The same notes say the mark on a weak vowel, i or u, keeps it from merging with its neighbour. The two vowels then fall into separate syllables. Only ú and í do this job.

Word	Meaning	Syllables	Wiktionary IPA	Why it is spelled that way
continuo	continual	con.ti.nuo	/konˈtinwo/	No mark: nuo is one syllable
continúo	I continue	con.ti.nú.o	/kontiˈnuo/	ú splits the u from the o
continuó	he or she continued	con.ti.nuó		Stress on the final vowel
baúl	trunk, chest	ba.úl	/baˈul/	ú splits the a from the u
búho	owl	bú.ho	/ˈbuo/	ú splits the u from the o, h or no h
reúne	meets, gathers	re.ú.ne	/reˈune/	ú splits the e from the u

The mark can move inside one verb. FundéuRAE (opens in a new tab) points out that reúne and reúnen carry it on the u, while reunió and reuniré do not. In those forms the stress has left the root. FundéuRAE calls reune without the mark inappropriate.

The commonest ú words in Spanish subtitles show both rules at work. Tú is the pronoun you; tu is your, and Wiktionary gives both the sound /tu/. Algún and ningún stress the last syllable and end in n. Único, última and número are stressed third from the end, so they always carry the mark.

Why does French keep ù for the single word où?

Of the u accents French uses, ù has the narrowest job: it is written in one word only. The Office québécois de la langue française (opens in a new tab) says the grave accent on a u appears only in où, the pronoun and adverb of place. Its purpose is to keep où apart from the conjunction ou. The office's own pair is "my brother or I" against "where should we go?".

You cannot hear the accent. Wiktionary transcribes où and ou alike as /u/. The mark exists for the reader alone, as in Wiktionary's example Où est la gare?, where is the station? Leave the accent off and the question starts with the word for or.

AccentPad's subtitle word data, from FrequencyWords, agrees. Où ranks among the most common words in French. The only other French entries with ù, sùr and dù, sit far down the tail. They are typos for sûr and dû, not words.

Italian is where ù does steady work. In the same data, its most frequent ù words all end in the letter: più, giù, laggiù, lassù and tribù. WikiPron transcribes più as /pju/ and giù as /d͡ʒu/.

Can you drop the circumflex from French û?

Mostly yes, since 1990, but not in a short list of words. The Académie française's annex on the rectifications (opens in a new tab) says the circumflex on i and u is no longer required. It stays in verb endings and where it brings a useful difference of meaning. The annex names dû, jeûne, the adjectives mûr and sûr, and the verb croître.

These are the pairs the hat keeps apart. The meanings and sounds come from Wiktionary.

Without the hat	With the hat	Sound
du, of the	dû, owed; past participle of devoir	/dy/ for both
sur, on	sûr, sure	/syʁ/ for both
mur, wall	mûr, ripe	/myʁ/ for both
jeune, young	jeûne, a fast	/ʒœn/; jeûne also /ʒøn/

In most pairs the hat changes no sound, like the grave of où. Jeûne is the exception. Wiktionary lists a closed /ʒøn/ for it beside the /ʒœn/ of jeune.

Everywhere else the hat may go, and the annex narrows the exception further. Mûr and sûr keep it only in the masculine singular. Derived words lose the protection, so sûr keeps the hat and sureté may drop it.

Traditional spelling	1990 spelling	Why
sûr	sûr	Kept: it tells sûr from sur
sûre	sure	Only the masculine singular keeps the hat
sûrement	surement	A derived word, outside the exception
dû	dû	Kept: it tells dû from du
goût	gout	No meaning to protect
brûler	bruler	No meaning to protect

Wiktionary lists gout, bruler and surement as post-1990 spellings. The Académie chose to recommend the new forms rather than impose them, so both spellings remain in use. In FrequencyWords, sûr and dû are the most frequent French words with û, ahead of sûre, sûrement, goût and brûler.

Which languages write a long u as ū, and which as ú?

Among the u accents, the macron and the acute both mark a long vowel: ū in Latvian and Lithuanian, ú in Czech, Hungarian and Irish. Wiktionary names the Latvian letter garais ū, long u, and the Lithuanian one u ilgoji. It gives both the sound /uː/. Irish calls its letter ú fada, long u. Czech ú is /uː/ too, and Czech spells the same sound ů, depending on its place in the word.

Language	Long u	What it is called	Example
Latvian	ū	garais ū
Lithuanian	ū	u ilgoji	lūpa, lip; sūnus, son
Lithuanian	ų	the nasal u	skųsti, lapų
Czech	ú or ů, by place in the word
Irish	ú	ú fada

The Lithuanian Encyclopedia (opens in a new tab) sets the short and long u side by side. Short u is in upė, river, and ugnis, fire. Long u is in lūpa and sūnus. Wiktionary transcribes upė as [ˈʊpʲeː] and lūpa as [ˈluːpɐ]. The encyclopedia adds a second spelling of the long vowel, ų, which records an old un. So a Lithuanian long u is either ū or ų.

Latvian took ū with its modern spelling. Wiktionary says a commission proposed it in 1908 and schools taught it from 1909. Wikidata's given names with ū include Šarūnas, Žydrūnas, Jokūbas and Artūrs.

Copy ū from the tiles at the top: it is the one u with accent that the Alt code table lacks, so on Windows the steps below use the emoji panel, and in Word the Alt+X code.