Noun

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

Adjective

• S: (adj) u ((chiefly British) of or appropriate to the upper classes especially in language use)