The Chinese word **坚硬** is formed through a **coordinative compound** structure, where two separate characters with closely related meanings are combined to reinforce and specify a single concept. The first character, **坚 (jiān)**, primarily conveys the idea of being solid, firm, or steadfast, often with a connotation of strength and durability. The second character, **硬 (yìng)**, specifically denotes physical hardness, rigidity, or toughness. When paired, they create a single, more emphatic adjective meaning "hard and solid," "unyielding," or "rock-hard," merging the notions of resilient firmness (**坚**) and tangible hardness (**硬**) into a term commonly used to describe materials like metal, stone, or even abstract qualities like a resolute will.