Definition of "antiparticle" [antiparticle]

• A subatomic particle, such as a positron, antiproton, or antineutron, having the same mass, average lifetime, spin, magnitude of magnetic moment, and magnitude of electric charge as the particle to which it corresponds but having the opposite sign of electric charge, opposite intrinsic parity, and opposite direction of magnetic moment. 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.

• "With similar methods an antiparticle to the neutron has subsequently been discovered, a discovery whose importance lies in the fact that the concept of the antiparticle was thereby extended to include also the neutral elementary particles."
• "And I’m no fan of the MP for Ladywood – though for years I considered her a kind of antiparticle Ann Widdicombe, whose honesty you can applaud even while disagreeing with her."
• "The history of antimatter begins with the physicist Paul Dirac whose work in the late 1920s established the fact that for every particle there is a corresponding antiparticle, exactly matching the particle but with opposite charge."