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(nē-hō′nē-əm, nĭ-)
n. Symbol Nh
An artificially produced radioactive element with atomic number 113 whose most stable isotopes have a mass number of 286 and 285, with half-lives of approximately 20 seconds and 5.5 seconds, respectively.

[Japanese Nihon, Japan (from Old Japanese, from Middle Chinese ŋit-pən', literally "(Land of the) Rising Sun" (source of modern Mandarin Rìběn, Japan) : ŋit, sun, from Old Chinese *nit; akin to Tibetan ñi-ma and Burmese ne + pən', root, stalk, origin, from Old Chinese *pənʔ, from Proto-Sino-Tibetan *pul) + -ium (so called because the element was first synthesized in 2004 by a research team at the Riken Institute in Japan). See Word History at Japan.]
American Heritage® Dictionary of the English Language, Fifth Edition. Copyright © 2016 by Houghton Mifflin Harcourt Publishing Company. Published by Houghton Mifflin Harcourt Publishing Company. All rights reserved.
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In 2016, four new elements were added to it: nihonium, moscovium, tennessine, and oganesson.
The name nihonium was derived from the Japanese word "Nihon," which means Japan.
The four elements confirmed by the International Union of Pure and Applied Chemistry are Nihonium (Nh), Moscovium (Mc), Tennessine (Ts) and Oganesson (Og).