noun, often attributive
pro·​tein | \ ˈprō-ˌtēn also ˈprō-tē-ən \

Definition of protein

1 : any of various naturally occurring extremely complex substances that consist of amino-acid residues joined by peptide bonds, contain the elements carbon, hydrogen, nitrogen, oxygen, usually sulfur, and occasionally other elements (such as phosphorus or iron), and include many essential biological compounds (such as enzymes, hormones, or antibodies)
2 : the total nitrogenous material in plant or animal substances

Examples of protein in a Sentence

You need more protein in your diet. These foods are an excellent source of protein. These foods have all of the essential proteins.
See More

Recent Examples on the Web

The metabolic breakdown of protein, fat, and fiber is a slower, more intricate process that both provides you with fuel from a biochemical POV, and the sensory experience of eating. Jaclyn London, Ms, Rd, Cdn, Good Housekeeping, "Celery Juice "Benefits" Are Total B.S., According to Nutrition Science," 16 Jan. 2019 The company hoped pharmaceutical companies and others would pay fees for the catalog of proteins, but a trend toward open-source sharing of such data made that plan untenable. James R. Hagerty, WSJ, "Peter Meldrum Helped Found Myriad Genetics to Find Genes Linked to Inherited Cancers," 28 Dec. 2018 While there is no added sugar, one serving packs 43 grams of carb, along with a gram of fat and a few grams of protein., "The 4 Healthiest Menu Items at Panera Bread (Plus 3 Things to Avoid)," 13 July 2018 Usually the wild animals are highly sought-after as popular sources of protein along with beef and pork, and cargo ships carrying the smoked meat arrive daily in the city, the trade hub for Congo’s northwestern Equateur province. Washington Post, "Congo’s Ebola outbreak poses challenges for bush meat," 17 June 2018 Enter this mix, a near perfect concoction of protein, fat, carbohydrates, and salt, minus the GI distress. Outside Online, "The Best Summer Race Kit of 2018," 15 May 2018 Ramen comes as classic or spicy tonkotsu, miso or vegetarian miso - or build a bowl of your own with a choice of protein, toppings, broth and add-ons. Nikki Delamotte,, "Lucky's Market opens second store in Ohio at Cleveland's Shoppes on Clifton (photos)," 15 May 2018 Meals are $7 or $8, depending on the size of the protein ordered. Michele Parente,, "San Diego's meal delivery and nutrition programs," 27 Apr. 2018 The versatile protein is both a dream and a nightmare. Audrey Bruno, SELF, "All the Different Ways to Thaw Chicken Breasts, Ranked," 5 Jan. 2019

These example sentences are selected automatically from various online news sources to reflect current usage of the word 'protein.' Views expressed in the examples do not represent the opinion of Merriam-Webster or its editors. Send us feedback.

See More

First Known Use of protein

1886, in the meaning defined at sense 1

History and Etymology for protein

French protéine, from Late Greek prōteios primary, from Greek prōtos first — more at proto-

Keep scrolling for more

Learn More about protein

Statistics for protein

Last Updated

23 Jan 2019

Look-up Popularity

Time Traveler for protein

The first known use of protein was in 1886

See more words from the same year

Keep scrolling for more

More Definitions for protein



English Language Learners Definition of protein

: a substance found in foods (such as meat, milk, eggs, and beans) that is an important part of the human diet


pro·​tein | \ ˈprō-ˌtēn \

Kids Definition of protein

: a nutrient found in food (as meat, milk, eggs, and beans) that is made up of many amino acids joined together, is a necessary part of the diet, and is essential for normal cell structure and function


noun, often attributive
pro·​tein | \ ˈprō-ˌtēn, ˈprōt-ē-ən \

Medical Definition of protein

1 : any of numerous naturally occurring extremely complex substances (as an enzyme or antibody) that consist of amino acid residues joined by peptide bonds, contain the elements carbon, hydrogen, nitrogen, oxygen, usually sulfur, and occasionally other elements (as phosphorus or iron), that are essential constituents of all living cells, that are synthesized from raw materials by plants but assimilated as separate amino acids by animals, that are both acidic and basic and usually colloidal in nature although many have been crystallized, and that are hydrolyzable by acids, alkalies, proteolytic enzymes, and putrefactive bacteria to polypeptides, to simpler peptides, and ultimately to alpha-amino acids
2 : the total nitrogenous material in plant or animal substances especially : crude protein

Keep scrolling for more

More from Merriam-Webster on protein

Rhyming Dictionary: Words that rhyme with protein

Spanish Central: Translation of protein

Nglish: Translation of protein for Spanish Speakers

Britannica English: Translation of protein for Arabic Speakers Encyclopedia article about protein

Comments on protein

What made you want to look up protein? Please tell us where you read or heard it (including the quote, if possible).


a complex dispute or argument

Get Word of the Day daily email!

Test Your Vocabulary

Homophone Quiz

  • three-bears-two-of-them-look-like-theyre-whispering-to-a-third-bear-who-looks-chuffed-to-be-the-center-of-attention
  • In order to judge how people felt, the senator's office hired a firm to take a ______.
Name That Thing

Test your visual vocabulary with our 10-question challenge!


Test Your Knowledge - and learn some interesting things along the way.


Love words? Need even more definitions?

Subscribe to America's largest dictionary and get thousands more definitions and advanced search—ad free!