u meaning and definition

U noun

Definition of U (noun)

1. a base containing nitrogen that is found in RNA (but not in DNA) and derived from pyrimidine; pairs with adenine
   • synonyms: uracil
2. a heavy toxic silvery-white radioactive metallic element; occurs in many isotopes; used for nuclear fuels and nuclear weapons
   • synonyms: atomic number 92, uranium
3. the 21st letter of the Roman alphabet
4. the 21st letter of the Roman alphabet

U adjective

Definition of u (adjective)

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