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kid·ney (kĭdnē)
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n. pl. kid·neys
1. Anatomy Either one of a pair of organs in the dorsal region of the vertebrate abdominal cavity, functioning to maintain proper water and electrolyte balance, regulate acid-base concentration, and filter the blood of metabolic wastes, which are then excreted as urine.
2. The kidney of certain animals, eaten as food.
3. An excretory organ of certain invertebrates.
4. Temperament; kind: a person of the same kidney.

[Later Middle English kideney, possibly back-formation (on the model of Middle English ey, egg, and its usual plural eiren, eggs, probably influenced by the similarity of the rounded shape of kidneys to that of eggs) from Middle English kideneiren, plural of kideneire, kidney : kide-, perhaps meaning “belly” or “pod, capsule” (in reference to the renal capsule, a tough fibrous membrane surrounding the kidney and surrounded by a layer of fat; compare Modern English dialectal (southern England) kid, pod, peasecod, probably from Old English *cyde, and akin to Old English codd, bag, sack, peasecod) + neire, kidney (from Old English *nēore, from Germanic *neurōn-; akin to Greek nephros, kidney, and Latin (colloquial dialect of the ancient city of Praeneste, east of Rome) nefrōnēs, testicles).]

The American Heritage® Dictionary of the English Language, Fifth Edition copyright ©2020 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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