U.

名词 u.:

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

形容词 u.:

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