HSK 7-9
牢固
láogù形
firm; secure
工人再次检查绳结是否牢固。
Gōngrén zàicì jiǎnchá shéngjié shìfǒu láogù.
The worker checked again whether the knot was secure.
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Appears across levels (7-9) in the HSK 3.0 word list.