Definition of "subatomic particle" [subatomic particle]

• Any of various units of matter below the size of an atom, including the elementary particles and hadrons. (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.

• ""It's a subatomic particle with a mass in the quadrillions of AMUs," he said."
• "The bogus sound caroms harshly off the walls of the cavernous courtroom, ricocheting like a subatomic particle long after everyone has fallen silent."