Any of a subgroup of unstable mesons that consist of an electrically charged form with a mass 966 times that of an electron and a neutral form with a mass 974 times that of an electron, produced as a result of a high-energy particle collision. Also called K-meson. See Table at subatomic particle.
A meson that has a positive or negative charge and a rest mass of about 966 electron masses, or no charge and a rest mass of 974 electron masses
American Heritage(R) Dictionary of the English Language, Fifth Edition. Copyright (c) 2011 by Houghton Mifflin Harcourt Publishing Company. Published by Houghton Mifflin Harcourt Publishing Company. All rights reserved.
www.Collinsdictionary.com (c) HarperCollins Publishers Ltd 2016