p-3a answered your question: Idioms?
“Take a rain check”?
“Take a rain check?” means:
- In principle I would like to do the thing you are suggesting
- For some practical reason, I can’t do the thing now
- I want you to know that I do actually want to do the thing
- Can we do it at some yet-to-be-determined point in the future?
I think it’s a reference to a practice some stores have with sales:
- Sometimes they will advertise a sale
- And then run out of the thing that’s on sale
- And give people who want to buy it rain check, which is a piece of paper entitling them to buy the product at the sale price once it comes back in stock
- Most stores don’t do this anymore, but some do
I believe the origin is not to sales and running out of product, but outdoor events which had to be cancelled or postponed due to the weather, typically rain. Events like baseball games would be cancelled and everyone who had purchased a ticket would be given a replacement to be used at a later date (the exact policies varied).
Ah, ok. Do ball games still do that?