Proton: subatomic particle with a positive charge found in the nucleus (from Greek πρῶτον = "first" and the name of the English chemist William Prout)

Chimical element: substance composed of atoms having an identical atomic number.

Newton, Principia Mathematica (II.viii.3): "Corpus omne perseverare in statu suo quiescendi vel movendi uniformiter in directum, nisi quatenus a viribus impressis cogitur statum illum mutare."

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