myelin sheath myelin • myelinate · · · Info · Definitions · Synonyms · Characters · · myelin sheath · · Text Common · · Latin · · Scripts 13 · · Length 4 · · Syllables Definitions · · · (noun) a layer of myelin encasing (and insulating) the axons of medullated nerve fibers. Synonyms: medullary sheath, myelin sheath. · · Noun Definition 1 Synonyms · · · medullary sheath · · Synonym 1 Characters · · space U+0020 a latin small letter a U+0061 e latin small letter e U+0065 h latin small letter h U+0068 i latin small letter i U+0069 l latin small letter l U+006C m latin small letter m U+006D n latin small letter n U+006E s latin small letter s U+0073 t latin small letter t U+0074 y latin small letter y U+0079