proton

Short definition from Wiktionary

Noun

1. 1
   A positively charged subatomic particle forming part of the nucleus of an atom and determining the atomic number of an element, composed of two up quarks and a down quark.
2. 2
   A positively charged subatomic particle forming part of the nucleus of an atom and determining the atomic number of an element, composed of two up quarks and a down quark: The atomic nucleus of protium (hydrogen-1)
3. 3
   Synonym of primordium.