ekasilicon

from The Century Dictionary.

• noun In chem., the name given by Mendeléjeff to an element, the existence of which he predicted, occupying the same position in his fifth series that silicon does in the third. When this element was subsequently discovered it was named germanium.

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

• noun (Chem.) The name of a hypothetical element predicted and afterwards discovered and named germanium; -- so called because it was a missing analogue of the silicon group. See germanium, and cf. ekabor.

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

• noun chemistry, element, obsolete The name given by Dmitri Mendeleev to the predicted element lying below silicon in the periodic table — later named germanium.