堅

• Physical: Structural solidity, hardness, or denseness. Suggests durability and integrity (e.g., seasoned timber, packed earth).
• Functional: Fortification; the act of strengthening or removing weaknesses to prevent a breach.
• Psychological/Moral: Resoluteness, tenacity, and steadfastness of purpose.

Can function as a verb meaning to fortify, strengthen, or make firm.

• 堅 vs 硬: While both relate to hardness, 堅 emphasizes durability and integrity, whereas 硬 often implies stiffness or inflexibility.
• 堅 vs 剛: 剛 typically suggests strength associated with power, sharpness, or the hardness of metal; 堅 emphasizes resistance to being moved, broken, or penetrated.
• 堅 vs 定: 定 refers to the act of settling or fixing a position (stability as equilibrium); 堅 refers to the durability and strength of that position once it has been fixed.

Simplified variant: 坚

The inclusion of the 土 (earth) component reflects the root concept of "packed earth"—material compressed until it no longer shifts—which informs both the physical sense of solidity and the metaphorical sense of an unshakable will.

When translating the psychological sense, note that depending on context, this stability of purpose can be rendered as a virtue (constancy) or a flaw (obduracy).