n :  a silvery heavy radioactive polyvalent metallic element that is found esp. in pitchblende and uraninite and exists naturally as a mixture of three isotopes of mass number 234, 235, and 238 in the proportions of 0.006 percent, 0.71 percent, and 99.28 percent respectively - symbol U - see ELEMENTtable   .
 
 
 
Similar sounding terms:  uranium 235  uri·no·ma 
 
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