elementary particle ele·men·ta·ryparticle uncommon noun 1. a particle that is less complex than an atom; regarded as constituents of all matter Synonymselementary particlefundamental particlesubatomic particle Related words Broader terms particle Narrower terms antileptonantiparticleantiquarkhadronleptonquarkstrange particleweakly interacting massive particle Parts atom WordNet 2.1 (Princeton University). WordNet 2.1 Copyright Princeton University. All rights reserved.