An oath or promise of unshakeable loyalty and commitment, implying something that will last for an extremely long time, as if Mount Tai could be ground down into a whetstone and the Yellow River could be reduced to a mere belt.
这对新人发誓要砺山带河，相守一生。
The newly married couple vowed to be together forever, their commitment enduring through all changes, like Mount Tai ground down and the Yellow River reduced to a belt.
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