particle

A particle is a minute fragment or quantity of matter. In the physical sciences, the word is used to describe a small  object to which can be ascribed several physical or chemical properties such as volume or mass; subatomic particles such as protons or neutrons; and other elementary particles. The word is rather general in meaning, and is refined as needed by various scientific fields. Something that is composed of particles may be referred to as being particulate. However, the term particulate is most frequently used to refer to pollutants in the Earth's atmosphere, which are a suspension of unconnected particles, rather than a connected particle aggregation.