Essence
Pith, True Meaning
noun, の adjective
The marrow of reality is the true essence of life. If you look deep down into reality you might even find the true meaning of life! Hmm I wonder what that is... it probably has something to do with a certain two digit number. Oh well.
しんずい
This is a jukugo word that uses the on'yomi readings of the kanji. You should be able to read this on your own.
京料理の真髄はハモ料理だと思います。
I think the essence of Kyoto cooking is in eel dishes.