Japanese

Noun

骨髄 ‎(hiragana こつずい, romaji kotsuzui)

1. bone marrow
2. one's innermost depths, the bottom of one's heart
3. the most important point

References

1. ↑ 1998, NHK日本語発音アクセント辞典 (NHK Japanese Pronunciation Accent Dictionary) (in Japanese), Tōkyō: NHK, ISBN 978-4-14-011112-3