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.
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.
From the 詩経 line 我心匪石、不可転也: “My heart is not a stone that can be rolled.” It signifies a conviction that cannot be shifted.