Definition

1. Noun:

   • The 21st letter of the modern English alphabet: A letter, written in uppercase as "U" and lowercase as "u".
   • A representation of the sound /juː/ or /ʌ/: The speech sound associated with this letter, as in "use" (/juːz/) or "cup" (/kʌp/).
   • (Chemistry) Symbol for uranium: The chemical symbol for the radioactive metallic element uranium (atomic number 92).
   • (Biochemistry) Abbreviation for uracil: In molecular biology, a nitrogenous base found in RNA.

2. Adjective (chiefly British):

   • Upper-class; characteristic of the upper social class: Used to describe language, behavior, or style considered typical of the upper class, especially in contrast to "non-U" (non-upper-class).

Examples of Usage

• Noun:

  • The word "umbrella" starts with the letter u.
  • Uranium, represented by the symbol U, is used in nuclear reactors.
  • In RNA, u (uracil) pairs with adenine.

• Adjective:

  • Her pronunciation was considered very U.
  • Using the term "serviette" instead of "napkin" was once deemed non-U.

Advanced Usage

• "U-turn": A complete reversal of policy, opinion, or direction. (Note: This is a compound word listed separately as a variant).
• In academic grading: In some educational systems, "U" can stand for "Ungraded" or "Unclassified".

Variants and Related Words

• Uppercase U, Lowercase u: The two forms of the letter.
• U-bend: A pipe fitting shaped like the letter U.
• U-turn (n): A turn made by a vehicle to reverse its direction, resembling the shape of the letter U; figuratively, a complete change in plan or opinion.
• U-shaped (adj): Having a shape similar to the letter U.

Synonyms

• Uranium (when used as the chemical symbol).
• Uracil (when used as the biochemical abbreviation).
• Upper-class (for the adjectival sense).

Related Phrases and Idioms

• Mind your p's and q's (and u's): An extension of the idiom meaning to be careful about one's behavior or details, humorously including the letter 'u'. (Note: This is a playful, non-standard variant of the common idiom).

Adjective

1. (chiefly British) of or appropriate to the upper classes especially in language use

Noun

1. the 21st letter of the Roman alphabet
2. a heavy toxic silvery-white radioactive metallic element; occurs in many isotopes; used for nuclear fuels and nuclear weapons
3. a base containing nitrogen that is found in RNA (but not in DNA) and derived from pyrimidine; pairs with adenine