Proton (noun)

1. A subatomic particle with a positive charge found in the nucleus of an atom.
2. A basic unit of atomic matter.

Origin:

From greek protos "first".

Examples:

1. The number of protons in an atom's nucleus determines its atomic number and therefore its identity as a unique element.
2. The proton is one of the fundamental particles that make up matter.
3. The proton is a type of hadron, which are particles made up of quarks.
4. Proton therapy is a type of radiation therapy that uses protons to treat cancer.
5. In nuclear physics, protons are used to create energy through nuclear reactions.