uadj. (chiefly British) of or appropriate to the upper classes especially in language use ; Un. the 21st letter of the Roman alphabet ; Un. a heavy toxic silvery-white radioactive metallic element ; occurs in many isotopes ; used for nuclear fuels and nuclear weapons ; Un. a base containing nitrogen that is found in RNA (but not in DNA) and derived from pyrimidine ; pairs with adenine ; U-boatn. a submersible warship usually armed with torpedoes ; u-driven. a rented car ; U-shapedadj. shaped in the form of the letter U ; u-turnn. complete reversal of direction of travel ; U. S. Air Forcen. the airforce of the United States of America ; the agency that defends the United States through control and exploitation of air and space ; U. S. Armyn. the army of the United States of America ; the agency that organizes and trains soldiers for land warfare ; U. S. Army Special Forcesn. a division of the United States Army that is specially trained for guerilla fighting ; U. S. Coast Guardn. an agency of the Department of Transportation responsible for patrolling shores and facilitating nautical commerce ; U. S. Coden. a consolidation and codification by subject matter of the general and permanent laws of the United States ; is prepared and published by a unit of the United States House of Representatives ; U.K.n. a monarchy in northwestern Europe occupying most of the British Isles ; divided into England and Scotland and Wales and Northern Ireland ; `Great Britain' is often used loosely to refer to the United Kingdom ; U.S.n. the executive and legislative and judicial branches of the federal government of the United States ;
