HSK 7-9
不懈
búxiè形
untiring; unremitting; indefatigable
经过多年不懈努力她成功了。
Jīng guò duō nián bú xiè nǔ lì tā chéng gōng le.
She succeeded after years of unremitting effort.
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Appears across levels (7-9) in the HSK 3.0 word list.