The same.
Greek tauto, contraction of to auto, the same.
A tautology occurs when the same thing is said twice in different words; a tautomer (Greek meros, a share) is each of two or more isomers of a compound which exist together in equilibrium; a tautonym is a taxonomic name in which the same word is used for both the genus and species elements, for example Coccothraustes coccothraustes, the hawfinch.
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