- Stable elementary particles having the smallest known positive charge, found in the nuclei of all elements. The proton mass is less than that of a neutron. A proton is the nucleus of the light hydrogen atom, i.e., the hydrogen ion.
Definition from: MeSH via Unified Medical Language System at the National Library of Medicine
- A small, positively charged particle of matter found in the atoms of all elements.
National Cancer Institute
See also Understanding Medical Terminology.