endosteum
noun
end·os·te·um en-ˈdä-stē-əm 
plural endostea en-ˈdä-stē-ə
: the layer of vascular connective tissue lining the medullary cavities of bone
Word History
Etymology
New Latin, from end- + Greek osteon bone — more at osseous
First Known Use
circa 1881, in the meaning defined above
Medical Definition
endosteum
noun
end·os·te·um en-ˈdäs-tē-əm
plural endostea -tē-ə
: the layer of vascular connective tissue lining the medullary cavities of bone