na-adjective, noun
Describes physical objects, structures, or materials that are robust and resistant to damage or wear. Often used for buildings, containers, or equipment.
この金庫は非常に堅牢な作りだ。
This safe is very solidly built.
堅牢な橋が川にかかっている。
A sturdy bridge spans the river.
Compound of 堅 (firm, hard) and 牢 (prison, firm). The combination conveys the idea of being firmly constructed and resistant to breaking.