marrow · essence

1. Origins, structure, and basic meaning

• Structure: 髄 denotes marrow and, figuratively, an essence; the source lists only the on-reading ずい.
• Basic usage: 骨髄 is literal bone marrow, while 真髄 is the essence or true heart of an art or idea.

2. Common pitfalls and similar expressions

• 骨髄 / 真髄
  • 骨髄: This anatomical noun refers to the marrow found inside bones. Example: 医師は骨髄の働きを図で説明した。
  • 真髄: This word refers to the deepest essence of an art, idea, or other subject. Example: 長年の修行を通して芸の真髄を学んだ。