What is "celtium"

Celtium \Cel"ti*um\, n. [NL.] (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.

n. (context chemical element obsolete English) A supposed chemical element of the rare earth group (proposed symbol Ct), later determined to be identical to lutetium.