noun
steadfastness; unwavering conviction
A literary yojijukugo expressing a heart that does not change, like a stone that stays put rather than rolling. Rare in modern conversation; found in classical or formal writing.
彼の匪石之心は、どんな困難にも揺るがなかった。
His steadfast heart remained unshaken by any hardship.
不動心 is a more common term for an immovable mind or unshakable spirit, used in both everyday and martial contexts. 匪石之心 is a rare classical expression with a similar nuance but a more literary, poetic feel.
A yojijukugo of classical Chinese origin, literally 'heart not of stone' (匪 = not, 石 = stone, 之 = of, 心 = heart). The phrase alludes to the idea that a stone can roll and change, but a steadfast heart does not. The exact historical derivation is uncertain beyond the literal kanji meaning.