"You can rest assured that he's not dead"
I've heard this line from one TV Series.

Is this phrase means the same like "You can be sure..." ? If so, what's the difference between those phrases ?

And I know what means the verb "to assure" but what is "rest assure" exactly?

Thank you for the answers!

Question

"You can rest assured that he's not dead"
I've heard this line from one TV Series.

Is this phrase means the same like "You can be sure..." ? If so, what's the difference between those phrases ?

And I know what means the verb "to assure" but what is "rest assure" exactly?

Thank you for the answers!

Answer

They mean the same thing for all practical purposes.

The “rest assured” is referring to “you don’t have to stay up worrying, you can go to sleep.”

BTW, it’s not past tense. It refers to the present or the future. Rest right now or rest tonight.

Answer

It is essentially the same thing, though the phrasing of "rest assured" is only used in the past tense. We also don't really use it in everyday language, it is a bit dated overall.

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