- Any of a family of subatomic particles that participate in strong interactions, are composed of a quark and an antiquark, and have masses generally intermediate between leptons and baryons. See Table at subatomic particle. (noun)
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.