in:1. during a period of time

2. at the end of a period of time
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I found the definition of the preposition 'in' in the dictionary.

Does #1 mean 'within'?
When we use the use of #2?

3. Just remember to give it back in a week.
(Does 'in' in #3 mean #1 or #2 or 'within'? When do we use #2?)

4. I will be back in a week.
(Here, 'in' means #2, right?)

Does #1 mean 'within'? Yes

3. Just remember to give it back in a week.
(Does 'in' in #3 mean #1 or #2 or 'within'? Yes, but in this sentence, it could also mean #2.

4. I will be back in a week.
(Here, 'in' means #2, right?) Yes