U

  1. noun
    the 21st letter of the Roman alphabet
  2. noun
    a nitrogen-containing base found in RNA (but not in DNA) and derived from pyrimidine; pairs with adenine
  3. adjective
    (chiefly British) of or appropriate to the upper classes especially in language use
  4. noun
    a heavy toxic silvery-white radioactive metallic element; occurs in many isotopes; used for nuclear fuels and nuclear weapons