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to nod; to bow one's head in assent; to agree
彼の提案に皆が首肯いて賛成した。
Everyone nodded and agreed to his proposal.
説明を聞いた部長は深く首肯いた。
After hearing the explanation, the department manager nodded deeply.
学生たちは講師の話に首肯いている。
The students are nodding along to the lecturer's talk.