At the latest means no later than: please return the keys by Friday at the latest. Earlier is fine, later isn't. Even firmer: at the very latest. It usually pairs with by and a deadline.
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by + deadline + at the latest / at the very latest
- Please return the keys by Friday at the latest.
- We should hear from the venue tomorrow at the latest.
- The final names must arrive by noon at the very latest.
What changed
First versionPlease return the keys until Friday at the latest.
RevisionPlease return the keys by Friday at the latest.
Until also seems to mark the end of a period, so it slips in: until Friday. But until means all the time up to: keep the keys until Friday, and they stay with you till then. A deadline for finishing something takes by.
At last means finally: at last, the bus arrived. It looks similar but means something else. On Friday means on that exact day. By Friday at the latest means on Friday or earlier.
Your turn
Send the signed form ___ noon at the latest: it must arrive no later than that.
Show the answer
by — The form must arrive no later than noon: that's a deadline, so by. Until describes something that continues up to noon.
Politely ask someone to return a document or confirm attendance by a specific date, using at the latest.
Please confirm the number of guests by Wednesday at the latest.
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