坚硬
jiān yìng · HSK 7
hard
🪨 坚 firm + 硬 hard = doubly unyielding; both halves mean tough, so the word stacks them
坚 means firm or strong-willed; 硬 means physically hard or stiff. Put together they reinforce each other into hard, solid, unyielding. 硬 also shows up in 硬件 meaning hardware, the hard parts of a computer.
硬 — stone 石 + 更 (gēng, phonetic)
硬 is a semantic-phonetic compound. The left side 石 'stone' gives the meaning—stones are hard—while the right side 更 originally suggested the pronunciation. From the literal sense of stone-hardness, 硬 extended to mean firm, stiff, or stubborn in both physical and figurative uses.