1. Bone marrow.
2. The spinal cord.
3. 1. The inmost, choicest, or essential part; the pith.
   2. Strength or vigor; vitality.

[Middle English marow, from Old English mearg.]

The American Heritage® Dictionary of the English Language, Fourth Edition Copyright © 2007, 2000 by Houghton Mifflin Company. Updated in 2009. Published by Houghton Mifflin Company. All rights reserved.