To happen to coincide or agree with each other without prior consultation.
约相约。事先没有约定而相互一致。
《史记·平津侯主父列传》应对而皆动，不谋而俱起，不约而同会。”
They all had the same idea about the solution, as if by prior agreement.
Learn the next connected idiom: 不约而同 (bù yuē ér tóng) → 同舟共济 (tóng zhōu gòng jì)
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