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essence; quintessence; spirit; soul; heart; pith (and marrow)
武道の真髄を極めた。
He mastered the essence of martial arts.
彼の演技に芸術の真髄を感じた。
I felt the essence of art in his performance.
その言葉に人生の真髄が凝縮されていた。
The essence of life was condensed in those words.