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pro·tein (prōtēn, -tē-ĭn)
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n.
1.
Any of a group of complex organic macromolecules that contain carbon, hydrogen, oxygen, nitrogen, and usually sulfur and are composed of one or more chains of amino acids. Proteins are fundamental components of all living cells and include many substances, such as enzymes, hormones, and antibodies, that are necessary for the proper functioning of an organism. They are essential in the diet of animals for the growth and repair of tissue and can be obtained from foods such as meat, fish, eggs, milk, and legumes.
2.
a. A food that is composed of such macromolecules: What protein would you like for dinner: chicken or fish?
b. The portion of a food consisting of such macromolecules: Nuts contain significant quantities of protein.

[French protéine, from Late Greek prōteios, of the first quality, of the first rank (protein being so called because it is a primary substance from which biological organisms are formed), from Greek prōtos, first; see per1 in the Appendix of Indo-European roots.]

protein·aceous (prōtn-āshəs, prōtē-nā-), pro·teinic (prō-tēnĭk), pro·teinous (prō-tēnəs) adj.

The American Heritage® Dictionary of the English Language, Fifth Edition copyright ©2018 by Houghton Mifflin Harcourt Publishing Company. All rights reserved.
 

Indo-European & Semitic Roots Appendices

    Thousands of entries in the dictionary include etymologies that trace their origins back to reconstructed proto-languages. You can obtain more information about these forms in our online appendices:

    Indo-European Roots

    Semitic Roots

    The Indo-European appendix covers nearly half of the Indo-European roots that have left their mark on English words. A more complete treatment of Indo-European roots and the English words derived from them is available in our Dictionary of Indo-European Roots.

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