my·e·lin 
(mīə-lĭn) also my·e·line (-lĭn, -lēn′)
(mīə-lĭn) also my·e·line (-lĭn, -lēn′)n.
A white fatty material, composed chiefly of lipids and lipoproteins, that encloses certain axons and nerve fibers. Also called medulla.
my′e·linic adj.