elementary particle
From Longman Dictionary of Contemporary EnglishRelated topics: Physicselementary particleˌelementary ˈparticle noun [countable] technicalHP one of the types of pieces of matter including electrons, protons, and neutrons that make up atomsExamples from the Corpuselementary particle• It was expected that a similar equation would govern the proton, the only other supposedly elementary particle known at that time.