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to close up; to shut up (e.g. behind doors)
to cut off (e.g. because a deadline has expired); to close off (e.g. subscription list)
今月末で受付を〆切る予定だ。
We plan to close registration at the end of this month.
募集人数に達したので応募を〆切った。
Applications were closed because the quota was reached.
定員になり次第、参加受付を〆切ります。
Registration will close as soon as capacity is reached.