The deadline for the report is next Monday.
応募の締切を一週間延長しました。
We extended the application deadline by one week.
closing up; keeping closed
Only when written 閉め切り / 閉切り
Refers to the act or state of closing something off, especially doors, windows, or a room. The spelling 閉め切り makes this physical closing sense clearer, though It is a search-only form.
暑い日は部屋の閉め切りを避け、こまめに換気してください。
On hot days, avoid keeping the room closed up and ventilate it frequently.
cofferdam
Civil-engineering term for a temporary watertight enclosure or barrier used to keep water out of a work area. Often written compactly as 締切 in technical contexts.
川の中に締切を設けて、橋脚の工事を行った。
They built a cofferdam in the river and carried out the pier construction.
I just barely made the deadline for the report.
Meeting deadlines is a basic part of the job.
The application deadline has already passed.
I was late for the manuscript deadline and apologized to the editor.
Since there weren't many participants, they decided to extend the deadline.
Attested shorthand spelling for the deadline sense; useful for recognition and search, but not the main learner spelling.
Search-only shorthand variant of 〆切り for the deadline sense.
Attested spelling for physically closing something such as doors or windows; it is search-only.