n 1  :  a soft highly vascular modified connective tissue that occupies the cavities and cancellous part of most bones and occurs in two forms:  a  :  a whitish or yellowish marrow consisting chiefly of fat cells and predominating in the cavities of the long bones - called also yellow marrow   b  :  a reddish marrow containing little fat, being the chief seat of red blood cell and blood granulocyte production, and occurring in the normal adult only in cancellous tissue esp. in certain flat bones - called also red marrow   2  :  the substance of the spinal cord .
 
   
 
Similar sounding terms:  mbar  mer  mire  MMR 
 
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