Which definition of U do you mean?

  • U n the 21st letter of the Roman alphabet
  • U s (chiefly British) of or appropriate to the upper classes especially in language use
  • Uracil n a base containing nitrogen that is found in RNA (but not in DNA) and derived from pyrimidine; pairs with adenine
  • Uranium n a heavy toxic silvery-white radioactive metallic element; occurs in many isotopes; used for nuclear fuels and nuclear weapons