WordNet (r) 3.0 (2006):

elementary particle
    n 1: (physics) a particle that is less complex than an atom;
         regarded as constituents of all matter [syn: elementary
         particle, fundamental particle]

Moby Thesaurus II by Grady Ward, 1.0:

58 Moby Thesaurus words for "elementary particle":
   Kern, NMR, air, alpha particle, antibaryon, antilepton, antimeson,
   atom, atomic nucleus, atomic particle, atomic particles, baryon,
   beta particle, brute matter, building block, chemical element,
   component, constituent, earth, electron, element, elementary unit,
   fire, fundamental particle, hyle, hypostasis, lepton, material,
   material world, materiality, matter, meson, molecule, monad,
   natural world, nature, neutron, nuclear force,
   nuclear magnetic resonance, nuclear particle, nuclear resonance,
   nucleon, nucleosynthesis, nucleus, photon, physical world, plenum,
   proton, strangeness, strong interaction, stuff, substance,
   substratum, the four elements, triton, unit of being,
   valence electron, water