What does 'rest' mean in 'rest assured' and where else 'rest' can be used in this way? What is the different between it and 'to be assured'?
You may rest assured of that.
English Language Learners Stack Exchange is a question and answer site for speakers of other languages learning English. It only takes a minute to sign up.
Sign up to join this communityWhat does 'rest' mean in 'rest assured' and where else 'rest' can be used in this way? What is the different between it and 'to be assured'?
You may rest assured of that.
"Rest assured" is an idiomatic expression similar to "sleep well". When you have trouble on your mind, you sleep poorly, but if that trouble is resolved, you can have a restful sleep.
In the same way, "rest assured" figuratively means that when you next lie down to take a rest you can feel comfortable knowing that some issue will not be a problem.
You can rest assured that you will never again be baffled by the idiomatic expression "rest assured".
(Edit). The verb "rest" actually comes from two different languages trees (Old English/German and French/Latin). An alternate (and somewhat archaic) meaning of "rest" is "remain" from the French rester. It may be that "rest assured" actually means to "remain/stay/be assured" rather than "sleep assured".
Either way, this does not really change the meaning or usage of the phrase, but it is interesting to consider. Also it helps explain why there is little (if any) semantic difference between "rest assured" and "be assured". Because "rest assured" feels like a guarantee or a blessing, in some contexts it may sound better.
"rest assured" is formal and is used to calm somebody down so that they will not worry. It is usually used in the imperative or with "can". "rest" is close in meaning to "remain" or "stay":
The Oxford English Dictionary states that the meaning of "rest" in this phrase is "remain".
Below is a transcription of OED entry 3 for "rest":
rest: 3 remain or be left in a particular condition: rest assured.
"be assured" is used to express that the subject will obtain something for sure. Here follow some examples from the Longman dictionary:
• People do work without the institutional system of capitalism and they are assured of a reasonable livelihood.
• The team is assured of a spot in the finals.
• There was no reason for a playoff game because both were assured of advancing to the postseason.
• Cooke was a happier man when greeting the news that full-back Jon Webb is assured of completing the season.
• When he did, he was assured of immediate payment.
• Residents must be assured of their physical security before any region can grow.
• Only three of them secured enough votes to be assured of their seats.