What does proton mean?
A proton is a stable, positively charged subatomic particle found in atomic nuclei. It is not an elementary particle: modern physics describes it as a composite baryon containing two up quarks and one down quark. The nucleus of ordinary hydrogen consists of one proton, and a proton’s positive charge is balanced by negatively charged electrons in the surrounding atom. Protons occur in many scientific and medical applications, including nuclear research, particle accelerators, and proton therapy, in which a controlled beam of protons is used to treat certain cancers. The word also has a regional informal meaning in South Asian English: a proton is a person who strongly supports a proposal, policy, or candidate. This supporting sense derives from the same Greek root for “first” but is much less common internationally than the particle sense.
A positively charged composite subatomic particle found in atomic nuclei; a hydrogen-1 nucleus is the simplest example.
"The experiment accelerated protons to nearly the speed of light."
This is the dominant international meaning. In medicine, “proton” may refer to the particles used in proton therapy.
A person who supports or advocates a proposal, policy, cause, or candidate.
"She was the most vocal proton of the new policy among the party’s younger members."
Chiefly informal and characteristic of South Asian English.
The regular plural is used when referring to multiple particles or, in the regional supporter sense, multiple supporters.
"The chamber accelerated a stream of protons toward the target."
Every proton in your body contains a fraction of the same primordial energy that was present moments after the universe began.
Reviewed by Deb Chak, Editor. AI-assisted content curated by RJS Tech Solutions LLP.
Where does proton come from?
The word comes from the Greek prōton, a neuter form of prōtos meaning “first.” In scientific usage, it was chosen to name the positively charged nuclear particle because it was associated with the element hydrogen, whose nucleus is the simplest atom. The same Greek root underlies words such as protagonist, prototype, protocol, and protist.
Related word forms
How proton is actually used
In physics, “proton” is standard technical vocabulary and is also used informally in medicine for proton therapy. The sense meaning “supporter” is informal and regional, chiefly associated with Indian and Pakistani English.
Easily confused with proton
A photon is a particle of electromagnetic radiation, whereas a proton is a positively charged particle that forms part of an atomic nucleus.
A proton is a subatomic particle, while a protein is a large biological molecule made of amino acids.