bohr·i·um (bôr??-?m)n. Symbol Bh An artificially produced radioactive element with atomic number 107 for which isotopes have been observed with mass numbers ranging from 260 to 275, all of which decay by alpha-particle emission. The isotope with mass number 264 has the longest confirmed half-life (1.3 seconds), although longer half-lifes have been reported for some of its heavier isotopes. See Periodic Table.[After Niels Henrik David Bohr.]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.bohrium (?b??r??m) n (Elements & Compounds) a transuranic element artificially produced in minute quantities by bombarding 204Bi atoms with 54Cr nuclei. Symbol: Bh; atomic no: 107. Former names: element 107 or unnilseptium [C20: after Neils Bohr]Collins English Dictionary ? Complete and Unabridged, 12th Edition 2014 © HarperCollins Publishers 1991, 1994, 1998, 2000, 2003, 2006, 2007, 2009, 2011, 2014bohr·i·um (bôr??-?m) Symbol Bh A synthetic, radioactive element that is produced by bombarding bismuth with chromium ions. Its most stable isotope has a half-life of 0.44 second. Atomic number 107. See Periodic Table.The American Heritage® Student Science Dictionary, Second Edition. Copyright © 2014 by Houghton Mifflin Harcourt Publishing Company. Published by Houghton Mifflin Harcourt Publishing Company. All rights reserved.