firm and solid; stout and durable
A yojijukugo emphasizing robust construction and lasting strength, used for physical objects, structures, or abstract systems.
This bridge is built firm and solid, and is said to last a hundred years.
彼の主張は堅牢堅固で、誰も反論できなかった。
His argument was stout and durable; no one could refute it.
A yojijukugo combining 堅牢 (solid, sturdy) and 堅固 (firm, steadfast), both of which share the character 堅 (hard, firm). The exact historical derivation is uncertain, but it likely arose as an emphatic compound in literary or formal contexts.