Lutetium is a rare earth element that has a symbol of Lu and an atomic number of 71. It is a silvery-white metal that is used in nuclear medicine, electronic devices, and catalytic converters. However, there are some synonyms for the word lutetium that you may not be aware of. One of the synonyms is cassiopeium, which was the original name given to lutetium when it was first discovered in 1907. Another synonym is aldebaranium, which was proposed by some scientists in honor of the star Aldebaran. Lastly, there is also the synonym of lutecium, which is a variant spelling of the element's name.