proton (n.)

1920 in physics sense of "sub-atomic particle with a positive charge," coined by British physicist Ernest Rutherford (1871-1937) from noun use of Greek prōton, neuter of prōtos "first" (see proto-), on analogy of electron; supposedly because hydrogen (the nucleus of which, in its commonest form, consists of one proton) was hypothesized as a constituent of all the elements. The word was used earlier in embryology (1893) as a translation of German anlage ("fundamental thing") based on Aristotle's phrase he prote ousia to proton.