牢 + Complement
牢 (láo) means "firm," "secure," or "sturdy" and emphasizes that something is strong and unbreakable. It is often used in literary or formal four-character expressions. For example, 牢不可破 means "unbreakable" or "indestructible."
这个结扎得很牢,不容易松开。
Zhège jié zā de hěn láo, bù róngyì sōngkāi.
This knot is tied very tightly and is not easy to loosen.
两国之间的友谊牢不可破。
Liǎng guó zhī jiān de yǒuyì láo bù kě pò.
The friendship between the two countries is unbreakable.
把这个架子固定牢,别让它倒了。
Bǎ zhège jiàzi gùdìng láo, bié ràng tā dǎo le.
Secure this shelf firmly so it doesn't fall over.