u

• 英语字母表的第二十一个字母，是元音字母，可表示多种发音，包括双元音 /juː/ 和短元音 /ʌ/；在网络俚语中常代替单词“you”。也用作铀（化学元素）、U 形掉头、大学（缩写）以及序列中第二十一个的符号。

The twenty-first letter of the English alphabet and the fifth vowel, representing various sounds including the long /juː/ as in 'universe', the short /ʌ/ as in 'cup', and the tense /uː/ as in 'rude'. As a grapheme, 'U' is a comparatively late addition to widespread English use, often replacing the older 'ou' vowel pairing in American English spellings like 'color' and 'honor'. It functions as an abbreviation for 'you' in informal written communications, a designation for uranium in chemistry, and the symbol for 'university' or a U-turn.

1. The twenty-first letter of the English alphabetA1formal

   The uppercase or lowercase character (U, u) that constitutes the twenty-first symbol in the Latin-based English alphabet, classified as a vowel. It commonly represents the /juː/ phoneme, but it can also be a short /ʌ/ or long /uː/. In American English, it is often missing from spellings where British English retains it, such as 'colour/color' and 'favour/favor'.

   英文字母表的第二十一个字母

   • The word 'umbrella' starts with the letter U.
   • In American English, 'color' is spelled without a U.
   • The long U sound is heard in the word 'uniform'.
   • She wrote the lowercase u with a small tail.
   • The vowel U is sometimes called the 'Greek u' in classical contexts.

2. A text-speech abbreviation for 'you'A1slang

   The single letter U used as an informal phonetic abbreviation for the second-person pronoun 'you'. It is extremely common in text messaging, online chats, social media captions, and informal song lyrics to shorten messages and save space. Its usage is ubiquitous in internet slang but avoided in formal communication.

   你（网络俚语）

   • C U later!
   • I love U.
   • How R U doing?
   • txt me when U get home.
   • Y U no call me?

3. The chemical symbol for uraniumB1formalscientific

   The one-letter chemical symbol representing the element uranium, atomic number 92. It is a dense, silvery-white heavy metal in the actinide series. Uranium is weakly radioactive and best known for its use as fuel in nuclear power plants (specifically the isotope U-235) and in nuclear weapons. It was named after the planet Uranus.

   铀（化学元素）

   • Uranium, symbolized by U, is the main fuel for nuclear reactors.
   • The U-235 isotope is used in nuclear fission.
   • Miners extracted U ore from the deep mine.
   • Enriched U contains a higher percentage of the fissile isotope.
   • The atomic mass of U is approximately 238.

4. A designation for a U-turnB1informal

   The letter U used adjectivally to describe a 180-degree turn, resembling the shape of the uppercase letter. It is commonly used in traffic regulations, navigation, and colloquial speech to describe a complete reversal in policy, opinion, or direction. A 'U-turn' implies a sharp turn that takes the driver or situation back in the opposite direction.

   掉头（U 形转弯）

   • The driver made an illegal U-turn in the middle of the street.
   • The government's U-turn on tax policy surprised everyone.
   • The GPS said to take a U-turn at the next junction.
   • His career took a dramatic U-turn when he left banking for art.
   • No U-turn signs are posted at several intersections.

5. An abbreviation for universityA2informal

   The letter U used as an informal abbreviation for 'university', particularly in campus branding, sportswear, casual speech among students, and short-form writing such as text messages. While it is rarely used in formal academic writing without periods, it is a prominent feature in college logos and everyday student vocabulary.

   大学（缩写）

   • He's studying at the U of T next year.
   • The U bookstore sells official hoodies and shirts.
   • Go U! The football team won the championship!
   • I have a meeting at the U library this afternoon.
   • She pays U fees, which include health insurance.