noun, na-adjective
firm and solid; stout and durable
A yojijukugo emphasizing robust construction and lasting strength, used for physical objects, structures, or abstract systems.
この橋は堅牢堅固な造りで、百年はもつと言われている。
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.
堅牢 means 'solid' or 'sturdy', often used for physical objects; 堅牢堅固 combines it with 堅固 for a stronger, more formal expression.
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.