noun Biology.

a soft, white, fatty material in the membrane of Schwann cells and certain neuroglial cells: the substance of the myelin sheath.

Also my·e·line [mahy-uh-leen] /ˈmaɪ əˌlin/.

Origin of myelin

First recorded in 1865–70; myel- + -in2
Related formsmy·e·lin·ic, adjective Unabridged Based on the Random House Unabridged Dictionary, © Random House, Inc. 2019

Examples from the Web for myelin

Contemporary Examples of myelin

Historical Examples of myelin

  • Alveolar cells commonly contain fat-droplets and, less frequently, myelin globules.

  • Between the neurolemma and the axis cylinder is the medullated sheath, composed of a fatty substance known as myelin.

    Manual of Surgery

    Alexis Thomson and Alexander Miles

British Dictionary definitions for myelin


myeline (ˈmaɪɪˌliːn)


a white tissue forming an insulating sheath (myelin sheath) around certain nerve fibres. Damage to the myelin sheath causes neurological disease, as in multiple sclerosis
Derived Formsmyelinic, adjective
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

Word Origin and History for myelin

also myeline, "soft material found in nerve tissues," 1867, from German Myelin (1854), from Greek myelos "marrow; the brain, innermost part," of unknown origin.

Online Etymology Dictionary, © 2010 Douglas Harper

myelin in Medicine




A white fatty material composed chiefly of alternating layers of lipids and lipoproteins that encloses the axons of myelinated nerve fibers.
Droplets of lipid formed during autolysis and postmortem decomposition.
Related formsmy′e•linic adj.
The American Heritage® Stedman's Medical Dictionary Copyright © 2002, 2001, 1995 by Houghton Mifflin Company. Published by Houghton Mifflin Company.

myelin in Science



A whitish, fatty substance that forms a sheath around many vertebrate nerve fibers. Myelin insulates the nerves and permits the rapid transmission of nerve impulses. The white matter of the brain is composed of nerve fibers covered in myelin.
The American Heritage® Science Dictionary Copyright © 2011. Published by Houghton Mifflin Harcourt Publishing Company. All rights reserved.