B-s meson (b???s?)n. An electrically neutral meson composed of a strange quark and a bottom antiquark and having a mass about 10,500 times that of an electron and a mean lifetime of about 1.5 × 10-12 second.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.