definition of
U

[1] #1 U n. [uracil] a base containing nitrogen that is found in RNA (but not in DNA) and derived from pyrimidine; pairs with adenine. wn

[2] #2 U s. [u] (chiefly British) of or appropriate to the upper classes especially in language use. wn

[3] #3 U n. [uranium, atomic number 92] a heavy toxic silvery-white radioactive metallic element; occurs in many isotopes; used for nuclear fuels and nuclear weapons. wn

[4] #4 U n. [u] the 21st letter of the Roman alphabet. wn

[5] #5 U n. [u] the 21st letter of the Roman alphabet. wn