noun (n)

• a white fatty substance that forms a medullary sheath around the axis cylinder of some nerve fibers(noun.substance)

  Synonym:
  myelin, myeline
  

  source: wordnet30
• lower or hindmost part of the brain; continuous with spinal cord; (`bulb' is an old term for medulla oblongata)(noun.body)

  Example:
  The medulla oblongata is the most vital part of the brain because it contains centers controlling breathing and heart functioning.
  

  Synonym:
  bulb, medulla oblongata
  

  source: wordnet30
• the inner part of an organ or structure in plant or animal(noun.body)

  Antonym:
  cortex
  

  source: wordnet30
• Marrow; pith; hence, essence.(noun)

  source: webster1913