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