n. A doubling; duplication; repetition.n. Specifically In rhetoric, immediate repetition of a word, generally with added emphasis: asn. [Repetition after one or two intervening words is also accounted gemination: as, again and again.n. Also calleddiplasiasmus andepizeuxis.n. In philology: The doubling of an originally single consonant through the influence of a following consonant or vowel, as in Anglo-Saxon sittan(originally sitian), fenn(originally feni, Gothic fani), etc.; less properly used of mere orthographic doubling, as in hammer, matter, etc.n. A pair of letters so doubled.n. In astronomy, the frequent apparent doubling of the canals of Mars. It is still debated whether the phenomenon represents a real fact on the planet's surface or is merely optical or visual.n. In anatomy, the union or fusion of two contiguous teeth caused by the uniting of two tooth-pulps.