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[ker-uh-tin] /ˈkɛr ə tɪn/
a scleroprotein or albuminoid substance, found in the dead outer skin layer, and in horn, hair, feathers, hoofs, nails, claws, bills, etc.
Origin of keratin
First recorded in 1840-50; kerat- + -in2 Unabridged
Based on the Random House Dictionary, © Random House, Inc. 2018.
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British Dictionary definitions for keratin


a fibrous protein that occurs in the outer layer of the skin and in hair, nails, feathers, hooves, etc
Collins English Dictionary - Complete & Unabridged 2012 Digital Edition
© William Collins Sons & Co. Ltd. 1979, 1986 © HarperCollins
Publishers 1998, 2000, 2003, 2005, 2006, 2007, 2009, 2012
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Word Origin and History for keratin

basic substance of horns, nails, feathers, etc., 1847, from Greek keras (genitive keratos) "horn" (see kerato-) + chemical suffix -in (2).

Online Etymology Dictionary, © 2010 Douglas Harper
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keratin in Medicine

keratin ker·a·tin (kěr'ə-tĭn)
Any of a group of scleroproteins or albuminoids that contain large amounts of sulfur and are the chief structural constituents of hair, nails, and other horny tissues.

The American Heritage® Stedman's Medical Dictionary
Copyright © 2002, 2001, 1995 by Houghton Mifflin Company. Published by Houghton Mifflin Company.
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keratin in Science
Any of a class of tough, fibrous proteins that are the main structural component of hair, nails, horns, feathers, and hooves. Keratins are rich in sulfur-containing amino acids, especially cysteine. Individual keratin molecules are entwined helically around each other in long filaments, which are cross-linked by bonds between sulfur atoms on different chains. The twining and cross-linking produce strength and toughness.
The American Heritage® Science Dictionary
Copyright © 2002. Published by Houghton Mifflin. All rights reserved.
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