celtium

from the GNU version of the Collaborative International Dictionary of English.

• noun (Chem.) The first proposed name for a supposed new element of the rare-earth group, accompanying lutecium and scandium in the gadolinite earths. It is now considered identical to lutetium. The proposed symbol was Ct (no period), but this name and symbol are no longer used.

from Wiktionary, Creative Commons Attribution/Share-Alike License.

• noun chemistry A former name of hafnium.