a radioactive chemical element with a very short half-life: a transactinide produced by bombarding californium or berkelium with high-energy nuclear particles: symbol, Db; at. no., 105
See dubnium in American Heritage Dictionary 4
(do͞obˈnē-əm)
noun Symbol Db
An artificially produced radioactive element with atomic number 105 whose most long-lived isotopes have mass numbers of 258, 261, 262, and 263 with half-lives of 4.2, 1.8. 34, and 30 seconds, respectively. Also called unnilpentium. See Table at element.