protein

UK: /ˈprəʊtiːn/ US: /ˈproʊtin, -tiɪn/ ,(prō′tēn, -tē in)

WordReference Random House Learner's Dictionary of American English © 2026

pro•tein /ˈproʊtin, -tiɪn/   n. 

1. Biochemistry [countable] a molecule that is a large portion of the mass of every life form, composed of amino acids linked in long chains.
2. Nutrition plant or animal tissue rich in such molecules:
   [uncountable] Meat is a source of protein.
   [countable] various proteins.

WordReference Random House Unabridged Dictionary of American English © 2026

pro•tein  (prō′tēn, -tē in), n. 

1. Biochemistry any of numerous, highly varied organic molecules constituting a large portion of the mass of every life form and necessary in the diet of all animals and other nonphotosynthesizing organisms, composed of 20 or more amino acids linked in a genetically controlled linear sequence into one or more long polypeptide chains, the final shape and other properties of each protein being determined by the side chains of the amino acids and their chemical attachments: proteins include such specialized forms as collagen for supportive tissue, hemoglobin for transport, antibodies for immune defense, and enzymes for metabolism.
2. Nutrition the plant or animal tissue rich in such molecules, considered as a food source supplying essential amino acids to the body.
3. Biochemistry (formerly) a substance thought to be the essential nitrogenous component of all organic bodies.

adj. 

4. Biochemistry of the nature of or containing protein.

Also, pro•teid  (prō′tēd, -tē id). 

• French
• Greek prōte(îos) primary + German -in -in²; replacing proteine
• German Protein
• 1835–45;

pro•tein•a•ceous  (prō′tē nā′shəs, -tē i nā′-), pro•tein′ic, pro•tei′nous, adj. 

Collins Concise English Dictionary © HarperCollins Publishers::

protein / ˈprəʊtiːn/ noun

1. any of a large group of nitrogenous compounds of high molecular weight that are essential constituents of all living organisms. They consist of one or more chains of amino acids linked by peptide bonds and are folded into a specific three-dimensional shape maintained by further chemical bonding

Etymology: 19th Century: via German from Greek prōteios primary, from protos first + -in

ˌproteinˈaceous, proˈteinic, proˈteinous adjective