bone marrow

noun

1. marrow¹(def 1).

noun

1. See marrow 1 (def. 1)

n.

1. The soft, fatty, vascular tissue filling the cavities of bones, having a stroma of reticular fibers and cells.

1. The spongy, red tissue that fills the bone cavities of mammals. Bone marrow is the source of red blood cells, platelets, and most white blood cells.