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The prefix Dwi (from sanskr. Dwi "two") was used to designate chemical elements not yet discovered in the periodic table .

An element then got the name of an already known element together with the prefix Dwi if it was two periods below it and the element in between (with the prefix Eka ) was also not yet named. For example, until its discovery , rhenium was called dwi- manganese .

Today, instead of the prefixes Eka and Dwi, systematic element names according to the atomic number are used for elements that have not yet been named.