昨週 - when is it used? (compared with 先週)


Are they interchangeable, or is 昨週 an old way to say it, and not used as much
any more?

> 昨週レストランに友だちと行った。

If anybody knows any kind of nuances or differences, such as where one would
be more appropriate, it would be interesting to know. Thank you very much!




`昨週` is in a dictionary, but I have never heard the word. While
`昨週レストランに友だちと行った` is not necessarily incorrect, I think `先週` is the most
natural word for any instance. It's also confirmed by search results in
Google:

  * `先週` 24,800,000 results
  * `昨週` 11,200 results

There are no difference between `先週` and `昨週` in meaning. `昨週` does not seem
to be old-fashioned. It's just a rarely-used word.

