If you say you will take a rain check on an offer or suggestion, you mean that you do not want to accept it now, but you might accept it at another time.
I was planning to ask you in for a brandy, but if you want to take a rain check,that's fine.
Can I take a rain check on that?
2. countable noun
A rain check is a free ticket that is given to people when an outdoor game or event is stopped because of rain or bad weather, so that they can go to it when it is held again.
[US]
rain check in American English
US
1.
the stub of a ticket to a ballgame or other outdoor event, entitling the holder to be admitted at a future date if the original event is rained out
2.
an offer to renew or defer an unaccepted invitation or offer
3.
a coupon, issued by a store to a customer, which guarantees that an item that is on sale at a reduced price but has been sold out may be purchased by that customer in the future at the lower price