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