What does protein mean?
A protein is a large organic molecule made from one or more chains of amino acids. These molecules form the working machinery of living cells, performing structural, transport, signalling, enzymatic, and defensive functions. The word also has an everyday nutritional meaning: protein is the nutrient supplied by foods such as meat, fish, eggs, dairy products, beans, nuts, and seeds. In this sense, it is generally uncountable, as in “a diet high in protein,” although “proteins” can refer to individual molecular substances in scientific writing. The term comes from the Greek root associated with what is primary or first, reflecting the historical idea of proteins as fundamental substances of living matter. Protein is useful in both contexts because it connects ordinary eating habits with the complex chemistry that makes life possible.
nounA protein is a large organic molecule made of one or more chains of amino acids, produced by living cells and involved in virtually every biological process. In nutrition, protein is the class of nutrient found in foods such as meat, beans, dairy products, and eggs that supplies amino acids to the body.
- A large organic molecule composed of one or more chains of amino acids, with structural, enzymatic, transport, signalling, and defensive roles in living organisms.
- The nutrient found in foods such as meat, fish, eggs, dairy products, beans, nuts, and other foods, essential for growth and tissue maintenance.
"She added beans to the salad for extra protein and fiber."
"The test identified a protein in the blood that helps cells repair damaged DNA."
"Athletes often plan their meals around adequate protein intake and balanced meals."
Use the plural for individual biological molecules or distinct protein substances; protein is usually uncountable when referring to the nutrient or food category.
"The study compared the structures of two proteins involved in cell signalling."
Protein is both a vital nutrient and the molecular machinery of life: the same word describes dinner and the tiny workers running your cells.
Reviewed by Deb Chak, Editor. AI-assisted content curated by RJS Tech Solutions LLP.
Where does protein come from?
The word entered English in the 19th century through German, which had borrowed it from Greek. Its roots trace to Greek prōtos, meaning “first,” and forms associated with “primary” or “first,” reflecting an early chemical view of proteins as fundamental organic substances. The English word subsequently became established both in biology and nutrition, while related terms such as proteid, proteic, protease, and proteose developed from the same etymological tradition.
Related word forms
How protein is actually used
In scientific contexts, protein usually refers to an individual molecular substance and is countable: a protein, two proteins. In nutritional contexts, it is commonly uncountable when referring to the nutrient or food category: meat is rich in protein; she is increasing her protein intake. Pronunciation differs slightly between British and American English in the first vowel.
Easily confused with protein
Protein is a noun naming a biological molecule or nutrient, whereas protean is an adjective meaning changeable or highly versatile.