Main Entry: bone marrow

Function: noun

Date: 1893

: a soft highly vascular modified connective tissue that occupies the cavities of most bones and occurs in two forms: a : one that is yellowish, consists chiefly of fat cells, and is found especially in the cavities of long bones b : one that is reddish, is the chief site of blood cell formation, and occurs in the normal adult in cancellous tissue especially of certain flat bones —called also red marrow